Multi-region battery separators

ABSTRACT

Disclosed is a battery separator, comprising two fiber regions comprising glass fibers, and a middle fiber region disposed between them comprising larger average diameter fibers and specified amounts of silica, or fine fibers, or both; and processes for making the separator. Also disclosed is a battery separator, comprising a fiber region and either one or two silica-containing region(s) adjacent thereto, each of the regions containing a specified amount of silica; and processes for making the separator. Such separators are useful, e.g., in lead-acid batteries.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/018,931, filed Feb. 9, 2016, which is a continuation of U.S.application Ser. No. 14/486,459, filed Sep. 15, 2014, which areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The invention relates to batteries, battery separators, and relatedmethods.

BACKGROUND

Batteries are commonly used as energy sources. Typically, a batteryincludes a negative electrode and a positive electrode. The negative andpositive electrodes are often disposed in an electrolytic medium. Duringdischarge of a battery, chemical reactions occur wherein an activepositive electrode material is reduced and active negative electrodematerial is oxidized. During the reactions, electrons flow from thenegative electrode to the positive electrode through a load, and ions inthe electrolytic medium flow between the electrodes. To prevent directreaction of the active positive electrode material and the activenegative electrode material, the electrodes are mechanically andelectrically isolated from each other by a separator.

One type of battery is a lead-acid battery. In a lead acid battery, leadis usually an active negative electrode material, and lead dioxide isusually an active positive electrode material. (In a lead-acid battery,the electrodes are often referred to as “plates”.) Generally, lead acidbatteries also contain sulfuric acid, which serves as an electrolyte andparticipates in the chemical reactions.

A mat comprised of glass fibers may serve as a separator. The glass matseparator has a critical role in electrolyte filling. Any change in thephysical properties of this material can drastically change the qualityof the filled and formed battery. The separator structure, degree ofcompression and fiber composition have a significant influence on howwell an unfilled element will accept electrolyte. While high levels ofcompression are desirable for extended life, this may make the fillingand formation process more difficult. When the separator is compressed,the pore size is reduced, along with more restricted access to void, orempty volume in the separator. This will make the filling process moredifficult.

When electrolyte is added to the battery, the ideal situation is thatall areas are wetted as much as possible by the same amount andconcentration of acid so that there is perfectly uniform distribution ofelectrolyte throughout the plate stack when the filling process iscompleted. This ideal situation is difficult or impossible to achieve inpractice, as there is a dynamic competition between the separator andthe plate surfaces for the electrolyte. As the electrolyte penetratesinto the plate stack, it is held up by the separator (the capillaryforces tend to hold the electrolyte rather strongly), and at the sametime the electrolyte is depleted by the exothermic reaction of thesulfuric acid with the plate by the simple chemical reaction ofPbO+H₂SO₄=>PbSO₄+H₂O. As the liquid front penetrates deeper into thestack it becomes more dilute and also gets hotter, due to the exothermicreaction with the lead oxide. One of the likely threats is the formationof hydration shorts/dendrites. As the acid reacts with the lead oxide,the sulfuric acid electrolyte becomes progressively more dilute. Leadsulfate is relatively soluble in the hot electrolyte with low acidstrength and near neutral pH, and dissolved lead sulfate will diffuseinto the separator. This will hasten the formation of lead dendritesand/or hydration shorts. A short circuit may develop and be detectedduring formation, or more subtly the battery will fail prematurely inservice due to the formation of lead dendrites through the separatorstructure. If the filling process is poor or incomplete, individualcells may also have “dry areas” after filling. These poorly wetted areasmay include no acid or water (completely dry), dilute acid or justwater. These dry areas will slowly become wetted during and afterformation, but significant grid corrosion may result due to unformedactive material forcing all of the current to flow through the gridonly.

During discharge, the sulfuric acid in the electrolyte is consumed andwater is produced, diluting the acid concentration and causing thespecific gravity of the electrolyte to decrease. During charging,formation of lead and lead oxide in the negative and positive plates,respectively, results in release of pure sulfuric acid. Due to its highspecific gravity, the pure sulfuric acid tends to settle toward thebottom (or “stratify”) in the electrolyte, a phenomenon known as “acidstratification”. In a stratified battery, electrolyte concentrates atthe bottom, starving the upper part of the cell. The light acid on toplimits plate activation, promotes corrosion and reduces the performance,while the high acid concentration on the bottom makes the battery appearmore charged than it is and artificially raises the open-circuitvoltage.

Unfortunately, design or materials changes that improve batteryperformance and/or life, e.g., separators that exhibit resistance toacid stratification, generally may also tend to make proper filling moredifficult.

SUMMARY

There is a need for a battery separator that improves acid filling andtherefore improves battery performance and cycle life. A batteryseparator comprised of a middle fiber region of a specified thicknessand containing coarse fibers disposed between two peripheral fiberregions containing fine fibers (a “3-region separator”) can improve acidfilling and plate formation by enhancing the diffusion of acid towardthe interior region. As a result of improved wettability of such aseparator, the density or concentration of the sulfuric acid is, incertain embodiments, maintained at an approximately constant levelthroughout the bulk of the separator. As a result, a uniform amount andconcentration of acid is available for reaction with active material inthe plates, thereby leading to homogenous plate formation and uniformactive material utilization. This can lead to improved cycle life andreduced defect rate of the battery.

In some embodiments, the present invention encompasses the insight thatsuch a 3-region battery separator in which the middle regionadditionally contains fine fiber, silica or both can exhibit otheradvantages. For example, a 3-region battery separator in which themiddle region additionally contains a certain amount of fine fibers canexhibit a greater tensile strength while still providing an improvedacid filling speed. Additionally, a 3-region battery separator in whichthe middle region additionally contains a certain amount of silica canexhibit increased resistance against acid stratification while stillproviding an improved acid filling speed. Moreover, a 3-region batteryseparator in which the middle region additionally contains both acertain amount of fine fibers and a certain amount of silica can exhibita greater tensile strength and increased resistance against acidstratification while still providing an improved acid filling speed.

In some embodiments, the present invention encompasses the insight thata battery separator comprising a fiber region adjacent to a fiber regionhaving a certain amount of silica, or a fiber region disposed betweentwo such silica-containing regions, can exhibit advantages. For example,such a separator can exhibit increased resistance against acidstratification while still providing an improved acid filling speed.

In one aspect, the invention relates to a battery separator, comprising:a middle fiber region; a first peripheral fiber region; and a secondperipheral fiber region; wherein the middle fiber region comprisesfibers having an average diameter of greater than or equal to 2 μm, and(a) from about 1 to 50% by weight fibers having an average diameter fromabout 0.1 to less than 2 μm, or (b) from about 1 to about 40% by weightsilica, or (c) from about 1 to about 40% by weight fibers having anaverage diameter from about 0.1 to less than 2 μm, and from about 1 toabout 20% by weight silica; wherein each of the first and secondperipheral fiber regions independently comprises glass fibers having anaverage diameter of less than or equal to 2 μm; provided that theaverage diameter of the fibers of the middle fiber region is larger thanthe average diameter of the fibers of each of the first and secondperipheral fiber regions; wherein the middle fiber region is disposedbetween the first peripheral fiber region and second peripheral fiberregion; and wherein the thickness of the middle fiber region constitutes1-49% of the total fiber region thickness.

In one aspect, the invention relates to a battery separator, comprising:a middle fiber region; a first peripheral fiber region; and a secondperipheral fiber region; wherein the middle fiber region is disposedbetween the first peripheral fiber region and second peripheral fiberregion; wherein the separator is produced by a process described herein.

In one aspect, the invention relates to a lead-acid battery comprising anegative plate, a positive plate, and a battery separator disposedbetween the negative and positive plates, wherein the battery separatorcomprises: a middle fiber region; a first peripheral fiber region; and asecond peripheral fiber region; wherein the middle fiber regioncomprises fibers having an average diameter of greater than or equal to2 μm, and (a) from about 1 to 50% by weight fibers having an averagediameter from about 0.1 to less than 2 μm, or (b) from about 1 to about40% by weight silica, or (c) from about 1 to about 40% by weight fibershaving an average diameter from about 0.1 to less than 2 μm, and fromabout 1 to about 20% by weight silica; wherein each of the first andsecond peripheral fiber regions independently comprises glass fibershaving an average diameter of less than or equal to 2 μm; provided thatthe average diameter of the fibers of the middle fiber region is largerthan the average diameter of the fibers of each of the first and secondperipheral fiber regions; wherein the middle fiber region is disposedbetween the first peripheral fiber region and second peripheral fiberregion; and wherein the thickness of the middle fiber region constitutes1-49% of the total fiber region thickness.

In one aspect, the invention relates to a lead-acid battery comprising anegative plate, a positive plate, and a battery separator disposedbetween the negative and positive plates, wherein the battery separatorcomprises a middle fiber region; a first peripheral fiber region; and asecond peripheral fiber region; wherein the middle fiber region isdisposed between the first peripheral fiber region and second peripheralfiber region; wherein the separator is produced by a process describedherein.

In one aspect, the invention relates to a battery separator, comprising:a fiber region; and either (a) a silica-containing region adjacent tothe fiber region, or (b) a first silica-containing region and a secondsilica-containing region, wherein the fiber region is disposed betweenthe first silica-containing region and the second silica-containingregion; wherein the fiber region and each silica-containing regioncontains fibers having an average diameter from about 2 to about 25 μm;wherein the fiber region contains less than 2% (including 0%) by weightsilica; wherein each silica-containing region independently containsgreater than or equal to 2% by weight silica.

In one aspect, the invention relates to a lead-acid battery comprising anegative plate, a positive plate, and a battery separator disposedbetween the negative and positive plates, wherein the battery separatorcomprises: a fiber region; and either (a) a silica-containing regionadjacent to the fiber region, or (b) a first silica-containing regionand a second silica-containing region, wherein the fiber region isdisposed between the first silica-containing region and the secondsilica-containing region; wherein the fiber region and eachsilica-containing region contains fibers having an average diameter fromabout 2 to about 25 μm; wherein the fiber region contains less than 2%(including 0%) by weight silica; wherein each silica-containing regionindependently contains greater than or equal to 2% by weight silica.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows how tensile strength of a 3-region separator varies in themachine direction based on the amount of fine fiber in the middle fiberregion.

FIG. 2 shows how tensile strength of a 3-region separator varies in thecross direction based on the amount of fine fiber in the middle fiberregion.

FIG. 3 shows how surface area of the middle region of a 3-regionseparator varies based on the presence of silica, fine fiber, or bothsilica and fine fiber in the middle fiber region.

FIG. 4 shows how acid stratification in a 3-region separator variesbased on the presence of silica, fine fiber, or both silica and finefiber in the middle fiber region.

FIG. 5A shows the diffusion speed test apparatus for use with theprocedure described in Example 2. FIG. 5B shows the vacuum fillapparatus for use with the procedure described in Example 2.

FIG. 6 shows how vacuum fill time for a 3-region separator varies basedon the amount of fine fiber in the middle region.

FIG. 7 shows how vacuum fill time for a 3-region separator varies basedon the presence of silica, fine fiber, or both silica and fine fiber inthe middle region.

FIG. 8 shows the acid stratification apparatus for use with theprocedure described in Example 2.

FIG. 9 shows an exemplary density profile of two adjacent regions of a3-region separator formed in a multi-phase papermaking process.

FIGS. 10A-10D show exemplary embodiments of a 3-region separator.

DETAILED DESCRIPTION

Definitions

As used herein, “total fiber region thickness” refers to the sum of thethicknesses of the two peripheral fiber regions and the middle fiberregion.

As used herein, the “thickness” of a region refers to the distancemeasured perpendicularly to the plane of the region from one end of theregion to the opposite end of the region.

When a value is stated to be “between” two endpoints or “from” oneendpoint to another endpoint, the endpoints are intended to be included.For example, a value “between 2 and 20” or “from 2 to 20” includes both2 and 20 as well as the values between.

Unless otherwise specified, the terms “include”, “includes”,“including”, etc. are intended to be open-ended. That is, “including Aand B” means including but not limited to A and B.

Composition

In one aspect, the invention relates to a battery separator, comprising:a middle fiber region; a first peripheral fiber region; and a secondperipheral fiber region; wherein the middle fiber region comprisesfibers having an average diameter of greater than or equal to 2 μm; and(a) from about 1 to 50% by weight fibers having an average diameter fromabout 0.1 to less than 2 μm, or (b) from about 1 to about 40% by weightsilica, or (c) from about 1 to about 40% by weight fibers having anaverage diameter from about 0.1 to less than 2 μm, and from about 1 toabout 20% by weight silica; wherein each of the first and secondperipheral fiber regions independently comprises glass fibers having anaverage diameter of less than or equal to 2 μm; provided that theaverage diameter of the fibers of the middle fiber region is larger thanthe average diameter of the fibers of each of the first and secondperipheral fiber regions; wherein the middle fiber region is disposedbetween the first peripheral fiber region and second peripheral fiberregion; and wherein the thickness of the middle fiber region constitutes1-49% of the total fiber region thickness. In some embodiments, themiddle fiber region comprises glass fibers having an average diameter ofgreater than or equal to 2 μm. Here and throughout, average diameter offibers can be measured by techniques known in the art, e.g., usingscanning electron microscopy (SEM).

As used herein in respect to such a separator, the “end” of a regionrefers to: (a) in the case of the end of a peripheral fiber region thatis not adjacent to the middle fiber region, the outer surface of theperipheral fiber region, which may also be the outer surface of theseparator; (b) in the case where the middle fiber region is laminated toa peripheral fiber region, the surface of the region at the point oflamination; (c) in the case where one fiber region transitions intoanother, such as the result of multi-phase formation, the midpoint ofthe transition zone, as defined herein.

Middle and Peripheral Fiber Regions—Generally

As used herein, the designations “middle” and “peripheral” in referenceto the fiber regions of the separator are used in a relative sense. Thatis, the “peripheral” fiber regions are peripheral inasmuch as the“middle” fiber region is disposed between them. As noted above, theouter surface of the peripheral fiber region may also be the outersurface of the separator; however, it need not be. In some embodiments,the outer surface of the peripheral fiber region is the outer surface ofthe separator. In some embodiments, the separator comprises anadditional layer adjacent to a “peripheral” fiber region.

In one aspect, the invention relates to a battery separator, consistingessentially of: a middle fiber region; a first peripheral fiber region;and a second peripheral fiber region; wherein the middle fiber regioncomprises fibers having an average diameter of greater than or equal to2 μm; and (a) from about 1 to 50% by weight fibers having an averagediameter from about 0.1 to less than 2 μm, or (b) from about 1 to about40% by weight silica, or (c) from about 1 to about 40% by weight fibershaving an average diameter from about 0.1 to less than 2 μm, and fromabout 1 to about 20% by weight silica; wherein each of the first andsecond peripheral fiber regions independently comprises glass fibershaving an average diameter of less than or equal to 2 μm; provided thatthe average diameter of the fibers of the middle fiber region is largerthan the average diameter of the fibers of each of the first and secondperipheral fiber regions; wherein the middle fiber region is disposedbetween the first peripheral fiber region and second peripheral fiberregion; and wherein the thickness of the middle fiber region constitutes1-49% of the total fiber region thickness.

In part, the middle fiber region comprises fibers having an averagediameter of greater than or equal to 2 μm. In some embodiments, themiddle fiber region comprises fibers having an average diameter from 2to about 50 μm. In some embodiments, the middle fiber region comprisesfibers having an average diameter from 2 to about 20 μm. In someembodiments, the middle fiber region comprises fibers having an averagediameter from about 3 to about 20 μm. In some embodiments, the middlefiber region comprises fibers having an average diameter from about 3 toabout 18 μm. In some embodiments, the middle fiber region comprisesfibers having an average diameter from about 3 to about 15 μm. In someembodiments, the middle fiber region comprises fibers having an averagediameter from about 5 to about 15 μm. In some embodiments, the middlefiber region comprises fibers having an average diameter from about 7 toabout 15 μm. In some embodiments, the middle fiber region comprisesfibers having an average diameter from about 3 to about 12 μm. In someembodiments, the middle fiber region comprises fibers having an averagediameter from about 5 to about 12 μm. In some embodiments, the middlefiber region comprises fibers having an average diameter from about 7 toabout 12 μm. In some embodiments, the middle fiber region comprisesfibers having an average diameter from about 5 to about 10 μm. In someembodiments, the middle fiber region comprises fibers having an averagediameter from about 7 to about 9 μm. In some embodiments, the middlefiber region comprises fibers having an average diameter of greater thanor equal to 2 μm. In some embodiments, the middle fiber region comprisesfibers having an average diameter of greater than or equal to 3 μm. Insome embodiments, the middle fiber region comprises fibers having anaverage diameter of greater than or equal to 5 μm. In some embodiments,the middle fiber region comprises fibers having an average diameter ofgreater than or equal to 7 μm.

In part, the middle fiber region comprises fibers having an averagediameter of greater than or equal to 2 μm. In some embodiments, themiddle fiber region comprises glass fibers having an average diameter ofgreater than or equal to 2 μm. In some embodiments, the middle fiberregion comprises glass fibers having an average diameter from 2 to about50 μm. In some embodiments, the middle fiber region comprises glassfibers having an average diameter from 2 to about 20 μm. In someembodiments, the middle fiber region comprises glass fibers having anaverage diameter from about 3 to about 20 μm. In some embodiments, themiddle fiber region comprises glass fibers having an average diameterfrom about 3 to about 18 μm. In some embodiments, the middle fiberregion comprises glass fibers having an average diameter from about 5 toabout 15 μm. In some embodiments, the middle fiber region comprisesglass fibers having an average diameter from about 7 to about 15 μm. Insome embodiments, the middle fiber region comprises glass fibers havingan average diameter from about 3 to about 12 μm. In some embodiments,the middle fiber region comprises glass fibers having an averagediameter from about 5 to about 12 μm. In some embodiments, the middlefiber region comprises glass fibers having an average diameter fromabout 7 to about 12 μm. In some embodiments, the middle fiber regioncomprises glass fibers having an average diameter from about 5 to about10 μm. In some embodiments, the middle fiber region comprises glassfibers having an average diameter from about 7 to about 9 μm. In someembodiments, the middle fiber region comprises glass fibers having anaverage diameter of greater than or equal to 2 μm. In some embodiments,the middle fiber region comprises glass fibers having an averagediameter of greater than or equal to 3 μm. In some embodiments, themiddle fiber region comprises glass fibers having an average diameter ofgreater than or equal to 5 μm. In some embodiments, the middle fiberregion comprises glass fibers having an average diameter of greater thanor equal to 7 μm.

The average diameter of the glass fibers in the first peripheral fiberregion can be the same or different from the average diameter of theglass fibers in the second peripheral fiber region, as long as eachaverage diameter is within the specified range. In some embodiments,each of the first and second peripheral fiber regions independentlycomprises glass fibers having an average diameter from about 0.1 toabout 2 μm. In some embodiments, each of the first and second peripheralfiber regions independently comprises glass fibers having an averagediameter from about 0.4 to about 1.8 μm. In some embodiments, each ofthe first and second peripheral fiber regions independently comprisesglass fibers having an average diameter from about 0.6 to about 1.6 μm.In some embodiments, each of the first and second peripheral fiberregions independently comprises glass fibers having an average diameterfrom about 0.8 to about 1.6 μm. In some embodiments, each of the firstand second peripheral fiber regions independently comprises glass fibershaving an average diameter from about 1.0 to about 1.6 μm. In someembodiments, each of the first and second peripheral fiber regionsindependently comprises glass fibers having an average diameter fromabout 1.2 to about 1.6 μm. In some embodiments, each of the first andsecond peripheral fiber regions independently comprises glass fibershaving an average diameter from about 0.4 to about 1.6 μm. In someembodiments, each of the first and second peripheral fiber regionsindependently comprises glass fibers having an average diameter fromabout 0.4 to about 1.4 μm. In some embodiments, each of the first andsecond peripheral fiber regions independently comprises glass fibershaving an average diameter from about 0.4 to about 1.2 μm. In someembodiments, each of the first and second peripheral fiber regionsindependently comprises glass fibers having an average diameter fromabout 0.4 to about 1.0 μm. In some embodiments, each of the first andsecond peripheral fiber regions independently comprises glass fibershaving an average diameter from about 0.4 to about 0.8 μm. In someembodiments, each of the first and second peripheral fiber regionsindependently comprises glass fibers having an average diameter fromabout 1.0 to about 1.4 μm. In some embodiments, each of the first andsecond peripheral fiber regions independently comprises glass fibershaving an average diameter of less than or equal to 1.8 μm. In someembodiments, each of the first and second peripheral fiber regionsindependently comprises glass fibers having an average diameter of lessthan or equal to 1.6 μm. In some embodiments, each of the first andsecond peripheral fiber regions independently comprises glass fibershaving an average diameter of less than or equal to 1.4 μm. In someembodiments, each of the first and second peripheral fiber regionsindependently comprises glass fibers having an average diameter of lessthan or equal to 1.2 μm. In some embodiments, each of the first andsecond peripheral fiber regions independently comprises glass fibershaving an average diameter of less than or equal to 1.0 μm. In someembodiments, each of the first and second peripheral fiber regionsindependently comprises glass fibers having an average diameter of lessthan or equal to 0.8 μm.

Middle Fiber Region

In some embodiments, the thickness of the middle fiber regionconstitutes 1-49% of the total fiber region thickness. In someembodiments, the thickness of the middle fiber region constitutes 2-48%of the total fiber region thickness. In some embodiments, the thicknessof the middle fiber region constitutes 3-47% of the total fiber regionthickness. In some embodiments, the thickness of the middle fiber regionconstitutes 1-45% of the total fiber region thickness. In someembodiments, the thickness of the middle fiber region constitutes 5-45%of the total fiber region thickness. In some embodiments, the thicknessof the middle fiber region constitutes 5-40% of the total fiber regionthickness. In some embodiments, the thickness of the middle fiber regionconstitutes 5-35% of the total fiber region thickness. In someembodiments, the thickness of the middle fiber region constitutes 5-30%of the total fiber region thickness. In some embodiments, the thicknessof the middle fiber region constitutes 5-25% of the total fiber regionthickness. In some embodiments, the thickness of the middle fiber regionconstitutes 10-45% of the total fiber region thickness. In someembodiments, the thickness of the middle fiber region constitutes 10-40%of the total fiber region thickness. In some embodiments, the thicknessof the middle fiber region constitutes 10-35% of the total fiber regionthickness. In some embodiments, the thickness of the middle fiber regionconstitutes 10-30% of the total fiber region thickness. In someembodiments, the thickness of the middle fiber region constitutes 10-25%of the total fiber region thickness.

The middle fiber region can comprise or be a part of a woven ornon-woven fiber web. In some embodiments, the middle fiber regioncomprises or is a part of a non-woven fiber web. In some embodiments,the middle fiber region comprises or is a part of a woven fiber web.

Middle Fiber Region: Coarse Fibers

In some embodiments, fibers having an average diameter from 2 to about50 μm account for a specified percentage by weight of the middle fiberregion. In some embodiments, fibers having an average diameter from 2 toabout 50 μm, 2 to about 20 μm, about 3 to about 20 μm, about 3 to about18 μm, about 3 to about 15 μm, about 5 to about 15 μm, about 7 to about15 μm, about 3 to about 12 μm, about 5 to about 12 μm, about 7 to about12 μm, about 5 to about 10 μm, about 7 to about 9 μm, greater than orequal to 2 μm, greater than or equal to 3 μm, greater than or equal to 5μm, or greater than or equal to 7 μm account for at least 10%, at least15%, at least 20%, at least 25%, at least 30%, at least 35%, at least40%, at least 45%, at least 50%, at least 55%, at least 60%, at least65%, at least 70%, at least 75%, at least 80%, at least 85%, at least90%, at least 95%, or about 99% of the middle fiber region by weight.Fibers having each specified range of average diameter can account foreach specified percentage by weight of the middle fiber region. Forexample, fibers having an average diameter from about 5 to about 10 μmcan account for at least 50% by weight of the middle fiber region, etc.

In some embodiments, the fibers of the middle fiber region having anaverage diameter from 2 to about 50 μm are at least 5%, at least 10%, atleast 15%, at least 20%, at least 25%, at least 30%, at least 35%, atleast 40%, at least 45%, at least 50%, at least 55%, at least 60%, atleast 65%, at least 70%, at least 75%, at least 80%, at least 85%, atleast 90%, at least 95%, or about 100% glass fibers.

In some embodiments, the middle fiber region comprises polymeric fibers.In some embodiments, the fibers of the middle fiber region having anaverage diameter from 2 to about 50 μm are at least 5%, at least 10%, atleast 15%, at least 20%, at least 25%, at least 30%, at least 35%, atleast 40%, at least 45%, at least 50%, at least 55%, at least 60%, atleast 65%, at least 70%, at least 75%, at least 80%, at least 85%, atleast 90%, at least 95%, or about 100% polymeric fibers. The polymericfibers may be in the form of staple fibers or may form a scrim.

In some embodiments, glass fibers having an average diameter from 2 toabout 50 μm account for a specified percentage by weight of the middlefiber region. In some embodiments, glass fibers having an averagediameter from 2 to about 50 μm, 2 to about 20 μm, about 3 to about 20μm, about 3 to about 18 μm, 3 to about 15 μm, about 5 to about 15 μm,about 7 to about 15 μm, about 3 to about 12 μm, about 5 to about 12 μm,about 7 to about 12 μm, about 5 to about 10 μm, about 7 to about 9 μm,greater than or equal to 2 μm, greater than or equal to 3 μm, greaterthan or equal to 5 μm, or greater than or equal to 7 μm account for atleast 10%, at least 15%, at least 20%, at least 25%, at least 30%, atleast 35%, at least 40%, at least 45%, at least 50%, at least 55%, atleast 60%, at least 65%, at least 70%, at least 75%, at least 80%, atleast 85%, at least 90%, at least 95%, or about 99% of the middle fiberregion by weight. Glass fibers having each specified range of averagediameter can account for each specified percentage by weight of themiddle fiber region. For example, glass fibers having an averagediameter from about 5 to about 10 μm can account for at least 50% byweight of the middle fiber region, etc.

Middle Fiber Region: Fine Fibers

In some embodiments, the middle fiber region comprises a specifiedamount (e.g., from about 1 to about 50% by weight) of fibers having anaverage diameter from about 0.1 to less than 2 μm. In some embodiments,these fibers have an average diameter from about 0.1 to about 0.8 μm. Insome embodiments, these fibers have an average diameter from about 0.8to about 1.6 μm. In some embodiments, these fibers have an averagediameter from about 1.4 to about 1.9 μm. In some embodiments, thesefibers have an average diameter from about 0.3 to about 1.9 μm. In someembodiments, these fibers have an average diameter from about 0.5 toabout 1.8 μm. In some embodiments, these fibers have an average diameterfrom about 0.8 to about 1.8 μm. In some embodiments, these fibers havean average diameter from about 1.0 to about 1.7 μm. In some embodiments,these fibers have an average diameter from about 1.2 to about 1.6 μm. Insome embodiments, these fibers have an average diameter from about 1.3to about 1.5 μm. In some embodiments, these fibers have an averagediameter of about 1.4 μm.

In some embodiments, the middle fiber region comprises a specifiedamount (e.g., from about 1 to about 50% by weight) of glass fibershaving an average diameter from about 0.1 to less than 2 μm. In someembodiments, these glass fibers have an average diameter from about 0.1to about 0.8 μm. In some embodiments, these glass fibers have an averagediameter from about 0.8 to about 1.6 μm. In some embodiments, theseglass have an average diameter from about 1.4 to about 1.9 μm. In someembodiments, these glass fibers have an average diameter from about 0.3to about 1.9 μm. In some embodiments, these glass fibers have an averagediameter from about 0.5 to about 1.8 μm. In some embodiments, theseglass fibers have an average diameter from about 0.8 to about 1.8 μm. Insome embodiments, these glass fibers have an average diameter from about1.0 to about 1.7 μm. In some embodiments, these glass fibers have anaverage diameter from about 1.2 to about 1.6 μm. In some embodiments,these glass fibers have an average diameter from about 1.3 to about 1.5μm. In some embodiments, these glass fibers have an average diameter ofabout 1.4 μm.

In some embodiments, the fibers of the middle fiber region having anaverage diameter from about 0.1 to less than 2 μm are at least 5%, atleast 10%, at least 15%, at least 20%, at least 25%, at least 30%, atleast 35%, at least 40%, at least 45%, at least 50%, at least 55%, atleast 60%, at least 65%, at least 70%, at least 75%, at least 80%, atleast 85%, at least 90%, at least 95%, or about 100% glass fibers.

Middle Fiber Region: Silica

In some embodiments, the middle fiber region comprises a specifiedamount (e.g., from about 1 to about 40% by weight) of silica. The silicacan be precipitated silica, colloidal silica and/or fumed silica. Thesilica has a surface area of at least 5 m²/g, e.g., from about 50 toabout 750 m²/g, from about 100 to about 700 m²/g, from about 150 toabout 650 m²/g, from about 200 to about 600 m²/g, from about 200 toabout 550 m²/g, from about 200 to about 500 m²/g, from about 300 toabout 500 m²/g, or from about 400 to about 500 m²/g. The averageparticle size of the silica can be from about 0.001 to about 20 μm,e.g., from about 1 to about 20 μm, or from about 10 to about 20 μm. Insome embodiments, the silica is precipitated silica. In someembodiments, the silica is precipitated silica having a surface areafrom about 50 to about 750 m²/g, from about 100 to about 700 m²/g, fromabout 150 to about 650 m²/g, from about 200 to about 600 m²/g, fromabout 200 to about 550 m²/g, from about 200 to about 500 m²/g, fromabout 300 to about 500 m²/g, or from about 400 to about 500 m²/g. Insome embodiments, the silica is precipitated silica having an averageparticle size from about 0.001 to about 20 μm, from about 1 to about 20μm, or from about 10 to about 20 μm. In some embodiments, the silica isprecipitated silica having a surface area from about 50 to about 750m²/g, from about 100 to about 700 m²/g, from about 150 to about 650m²/g, from about 200 to about 600 m²/g, from about 200 to about 550m²/g, from about 200 to about 500 m²/g, from about 300 to about 500m²/g, or from about 400 to about 500 m²/g, and having an averageparticle size from about 0.001 to about 20 μm, from about 1 to about 20μm, or from about 10 to about 20 μm. In some embodiments, the silica isprecipitated silica having a surface area from about 200 to about 500m²/g and an average particle size from about 1 to about 20 μm. In someembodiments, the silica is precipitated silica having a surface areafrom about 400 to about 500 m²/g and an average particle size from about10 to about 20 μm.

Middle Fiber Region Content: With Fine Fibers

In some embodiments, the middle fiber region contains fine fibers. Insome embodiments, fibers having an having an average diameter from about0.1 to less than 2 μm account for a specified percentage by weight ofthe middle fiber region. In some embodiments, fibers having an averagediameter from about 0.1 to less than 2 μm, about 0.1 to about 0.8 μm,about 0.8 to about 1.6 μm, about 1.4 to about 1.9 μm, about 0.3 to about1.9 μm, about 0.5 to about 1.8 μm, about 0.8 to about 1.8 μm, about 1.0to about 1.7 μm, about 1.2 to about 1.6 μm, about 1.3 to about 1.5 μm,or about 1.4 μm account for about 1 to 50%, about 2 to about 45%, about3 to about 40%, about 5 to about 40%, about 5 to about 35%, about 5 toabout 30%, about 5 to about 25%, about 10 to about 45%, about 10 toabout 40%, about 10 to about 35%, about 10 to about 30%, or about 10 toabout 25% of the middle fiber region by weight. Fibers having eachspecified range of average diameter can account for each specifiedpercentage by weight of the middle fiber region. For example, fibershaving an average diameter from about 0.8 to about 1.6 μm can accountfor about 10 to about 30% by weight of the middle fiber region, etc.

Middle Fiber Region Content: With Silica

In some embodiments, the middle fiber region contains silica. In someembodiments, silica accounts for a specified percentage by weight of themiddle fiber region. In some embodiments, silica accounts for about 1 toabout 40%, about 2 to about 40%, about 2 to about 35%, about 2 to about30%, about 2 to about 25%, about 2 to about 20%, about 2 to about 15%,about 5 to about 35%, about 5 to about 30%, about 5 to about 25%, about5 to about 20% or about 5 to about 15% of the middle fiber region byweight.

Middle Fiber Region Content: With Fine Fibers and Silica

In some embodiments, the middle fiber region contains both fine fibersand silica. In some embodiments, fibers having a specified averagediameter and silica each account for a specified percentage by weight ofthe middle fiber region. In some embodiments, fibers having an averagediameter from about 0.1 to less than 2 μm, about 0.1 to about 0.8 μm,about 0.8 to about 1.6 μm, about 1.4 to about 1.9 μm, about 0.3 to about1.9 μm, about 0.5 to about 1.8 μm, about 0.8 to about 1.8 μm, about 1.0to about 1.7 μm, about 1.2 to about 1.6 μm, about 1.3 to about 1.5 μm,or about 1.4 μm account for about 1 to 40%, about 2 to about 40%, about3 to about 40%, about 5 to about 40%, about 5 to about 35%, about 5 toabout 30%, about 5 to about 25% or about 5 to about 20% of the middlefiber region by weight, and silica accounts for about 1 to about 20%,about 1 to about 15%, about 2 to about 20%, about 2 to about 15%, about3 to about 20%, about 3 to about 15% or about 5 to about 15% of themiddle fiber region by weight. Fibers having each specified range ofaverage diameter can account for each specified percentage by weight ofthe middle fiber region, and independently silica can account for eachspecified percentage by weight of the middle fiber region. For example,fibers having an average diameter from about 0.3 to about 1.9 μm canaccount for about 1 to about 40% by weight and silica can account forabout 1 to about 20% by weight of the middle fiber region; fibers havingan average diameter from about 0.8 to about 1.8 μm can account for about5 to about 30% by weight and silica can account for about 2 to about 15%by weight of the middle fiber region; fibers having an average diameterfrom about 1.0 to about 1.7 μm can account for about 5 to about 25% byweight and silica can account for about 3 to about 15% by weight of themiddle fiber region; fibers having an average diameter from about 1.2 toabout 1.6 μm can account for about 5 to about 20% by weight and silicacan account for about 5 to about 15% by weight of the middle fiberregion; etc. In all such embodiments in which the middle fiber regioncontains both fine fibers and silica, the form, surface area andparticle size is as described above under “middle fiber region: silica”.

Peripheral Fiber Region

The thickness of the first peripheral fiber region can be the same ordifferent from the thickness of the second peripheral fiber region. Insome embodiments, the thickness of the first peripheral fiber region isfrom 70 to 130% of the thickness of the second peripheral fiber region.In some embodiments, the thickness of the first peripheral fiber regionis from 80 to 120% of the thickness of the second peripheral fiberregion. In some embodiments, the thickness of the first peripheral fiberregion is from 90 to 110% of the thickness of the second peripheralfiber region.

In some embodiments, glass fibers having a specified average diameteraccount for a specified percentage by weight of the either the first orthe second peripheral fiber region, or each peripheral fiber regionindependently. In some embodiments, glass fibers having an averagediameter from about 0.1 to about 2 μm, about 0.4 to about 1.8 μm, about0.6 to about 1.6 μm, about 0.8 to about 1.6 μm, about 1.0 to about 1.6μm, about 1.2 to about 1.6 μm, about 0.4 to about 1.6 μm, about 0.4 toabout 1.4 μm, about 0.4 to about 1.2 μm, about 0.4 to about 1.0 μm,about 0.4 to about 0.8 μm, about 1.0 to about 1.4 μm, less than or equalto 1.8 μm, less than or equal to 1.6 μm, less than or equal to 1.4 μm,less than or equal to 1.2 μm, less than or equal to 1.0 μm, or less thanor equal to 0.8 μm account for at least 10%, at least 15%, at least 20%,at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, atleast 50%, at least 55%, at least 60%, at least 65%, at least 70%, atleast 75%, at least 80%, at least 85%, at least 90%, at least 95%, orabout 100% of either the first or the second peripheral fiber region, oreach peripheral fiber region independently, by weight. Glass fibershaving each specified range of average diameter can account for eachspecified percentage by weight of either the first or the secondperipheral fiber region, or each peripheral fiber region independently.For example, glass fibers having an average diameter from about 0.4 toabout 1.8 μm can account for at least 50% by weight of either the firstor the second peripheral fiber region, or each peripheral fiber regionindependently, etc.

In some embodiments, the average glass fiber diameter of the firstperipheral fiber region differs from the average glass fiber diameter ofthe second peripheral fiber region by greater than or equal to 0.5, 0.6,0.7, 0.8, 0.9, 1.0, 1.1 or 1.2 μm. Each combination of average glassfiber diameter in each peripheral fiber region that permits thedifference in average fiber diameter to be achieved is contemplated. Forexample, each peripheral fiber region can have an average glass fiberdiameter of from about 0.4 to about 1.8 μm, provided that the averageglass fiber diameter of the first peripheral fiber region differs fromthe average glass fiber diameter of the second peripheral fiber regionby greater than or equal to 1.2 μm; each peripheral fiber region canhave an average glass fiber diameter of from about 0.8 to about 1.6 μm,provided that the average glass fiber diameter of the first peripheralfiber region differs from the average glass fiber diameter of the secondperipheral fiber region by greater than or equal to 0.5 μm; the firstperipheral fiber region can have an average glass fiber diameter of fromabout 0.4 to about 1.0 μm, and the second peripheral fiber region canhave an average glass fiber diameter of from about 1.0 to about 1.6 μm,provided that the average glass fiber diameter of the first peripheralfiber region differs from the average glass fiber diameter of the secondperipheral fiber region by greater than or equal to 0.7 μm; etc.

In some embodiments, the average pore size of the first peripheral fiberregion differs from the average pore size of the second peripheral fiberregion. In some embodiments, the average pore size of the firstperipheral fiber region differs from the average pore size of the secondperipheral fiber region by greater than or equal to 0.2 μm, 0.4 μm, 0.6μm, 0.8 μm, 1 pm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4μm, 2.6 μm, 2.8 μm or 3.0 μm. The pore size can be measured according tothe Battery Council International Standard BCIS-03a (Rev February 2002)method “Standard Test Method for Pore Size Characteristics by the LiquidPorosimetry Method Of Recombinant Battery Separator Mat” or “StandardTest Method for Pore Size Characteristics by the Mercury IntrusionMethod of Recombinant Battery Separator Mat”.

Either peripheral fiber region can comprise or be a part of a woven ornon-woven fiber web. In some embodiments, a peripheral fiber regioncomprises or is a part of a non-woven fiber web. In some embodiments,each of the first and second peripheral fiber regions comprises or is apart of a non-woven fiber web. In some embodiments, a peripheral fiberregion comprises or is a part of a woven fiber web. In some embodiments,each of the first and second peripheral fiber regions comprises or is apart of a woven fiber web.

Glass Fibers

In some embodiments, the glass fibers of any or all of the middle fiberregion and each of the peripheral fiber regions includes microglassfibers, chopped strand glass fibers, or a combination thereof.Microglass fibers and chopped strand glass fibers are known to thoseskilled in the art. One skilled in the art is able to determine whethera glass fiber is microglass or chopped strand by observation (e.g.,optical microscopy, electron microscopy). The terms refer to thetechnique(s) used to manufacture the glass fibers. Such techniquesimpart the glass fibers with certain characteristics. In general,chopped strand glass fibers are drawn from bushing tips and cut intofibers in a process similar to textile production. Chopped strand glassfibers are produced in a more controlled manner than microglass fibers,and as a result, chopped strand glass fibers will generally have lessvariation in fiber diameter and length than microglass fibers.Microglass fibers are drawn from bushing tips and further subjected toflame blowing or rotary spinning processes. In some cases, finemicroglass fibers may be made using a remelting process. In thisrespect, microglass fibers may be fine or coarse. As used herein, finemicroglass fibers are less than 1 μm in diameter and coarse microglassfibers are greater than or equal to 1 μm in diameter.

Microglass fibers may also have chemical differences from chopped strandglass fibers. In some cases, though not required, chopped strand glassfibers may contain a greater content of calcium or sodium thanmicroglass fibers. For example, chopped strand glass fibers may be closeto alkali free with high calcium oxide and alumina content. Microglassfibers may contain 10-15% alkali (e.g., sodium, magnesium oxides) andhave relatively lower melting and processing temperatures.

The microglass fibers can have small diameters such as less than 10.0μm. For example, the average diameter of the microglass fibers in aregion—as opposed to the average diameter of all the glass fibers in aregion—may be between 0.1 μm to about 9.0 μm; and, in some embodiments,between about 0.3 μm and about 6.5 μm, or between about 1.0 μm and 5.0μm. In certain embodiments, the microglass fibers may have an averagefiber diameter of less than about 7.0 μm, less than about 5.0 μm, lessthan about 3.0 μm, or less than about 1.0 μm. In certain embodiments,the microglass fibers may be subjected to a rotary spinning process andhave an average fiber diameter of between about 1.0 and about 10.0 μm,e.g., between about 3.0 and about 9.0 μm, between about 5.0 and about8.0 μm, between about 6.0 and about 10.0 μm, or between about 7.0 andabout 9.0 μm; or about 9.5 μm, about 9.0 μm, about 8.5 μm, about 8.0 μm,about 7.5 μm, about 7.0, about 7.0 μm, about 6.5 μm, about 6.0 μm, about5.5 μm, about 5.0 μm, about 4.5 μm, about 4.0 μm, about 3.5 μm, about3.0 μm, about 2.5 μm, about 2.0 μm, or about 1.5 μm. Average diameterdistributions for microglass fibers are generally log-normal. However,it can be appreciated that microglass fibers may be provided in anyother appropriate average diameter distribution (e.g., Gaussiandistribution, a distribution with a geometric standard deviation oftwice the average diameter, etc.).

The microglass fibers may vary significantly in length as a result ofprocess variations. In some embodiments, the microglass fibers have alength less than or equal to about 30 mm. In some embodiments, themicroglass fibers have a length less than or equal to about 6 mm. Insome embodiments, the microglass fibers have a length less than or equalto about 12 mm. In some embodiments, the microglass fibers have a lengthfrom about 6 mm to about 30 mm. The aspect ratios (length to diameterratio) of the microglass fibers in a region may be generally in therange of about 100 to 10,000. In some embodiments, the aspect ratio ofthe microglass fibers in a region are in the range of about 200 to 2500;or, in the range of about 300 to 600. In some embodiments, the averageaspect ratio of the microglass fibers in a region may be about 1,000; orabout 300. It should be appreciated that the above-noted dimensions arenot limiting and that the microglass fibers may also have otherdimensions.

Coarse microglass fibers, fine microglass fibers, or a combination ofmicroglass fibers thereof may be included within any particular region.In some embodiments, coarse microglass fibers make up between about 20%by weight and about 90% by weight of the glass fibers in the middlefiber region and/or one or both of the peripheral fiber regions. In somecases, for example, coarse microglass fibers make up between about 30%by weight and about 60% by weight of the glass fibers, or between about40% by weight and about 60% by weight of the glass fibers in the middlefiber region and/or one or both of the peripheral fiber regions. Forcertain embodiments that include fine microglass fibers, the finemicroglass fibers make up between about 0% and about 70% by weight ofthe glass fibers in the middle fiber region and/or one or both of theperipheral fiber regions. In some cases, for example, fine microglassfibers make up between about 5% by weight and about 60% by weight of theglass fibers, or between about 30% by weight and about 50% by weight ofthe glass fibers in the middle fiber region and/or one or both of theperipheral fiber regions.

The chopped strand glass fibers may have an average fiber diameter thatis greater than the diameter of the microglass fibers. In someembodiments, the chopped strand glass fibers have an average diameter ofgreater than about 5 μm. For example, the average diameter range may beup to about 30 μm. In some embodiments, the chopped strand glass fibersmay have an average fiber diameter between about 5 μm and about 12 μm.In certain embodiments, the chopped strand fibers may have an averagefiber diameter of less than about 10.0 μm, less than about 8.0 μm, lessthan about 6.0 μm. Average diameter distributions for chopped strandglass fibers are generally log-normal. Chopped strand diameters tend tofollow a normal distribution. Though, it can be appreciated that choppedstrand glass fibers may be provided in any appropriate average diameterdistribution (e.g., Gaussian distribution). In some embodiments, choppedstrand glass fibers may have a length in the range of between about0.125 inches and about 1 inch (e.g., about 0.25 inches, or about 0.5inches). In some embodiments, chopped strand glass fibers may have alength greater than or equal to 1 mm. In some embodiments, choppedstrand glass fibers may have a length in the range of between about 3 mmand about 24 mm.

It should be appreciated that the above-noted dimensions are notlimiting and that the microglass and/or chopped strand fibers may alsohave other dimensions.

In some embodiments, the separator has a combination of chopped strandglass fibers and microglass fibers. In some embodiments, the separatormay contain between about 0 weight percent to about 100 weight percentchopped strand glass fibers. In some embodiments, the separator maycontain between about 5 weight percent to about 15 weight percentchopped strand glass fibers. In some embodiments, the separator maycontain between about 0 weight percent to about 100 weight percentmicroglass fibers. In some embodiments, the separator may containbetween about 85 weight percent to about 95 weight percent microglassfibers. In some embodiments, the separator may contain between about 85weight percent to about 100 weight percent microglass fibers.

In some embodiments, the middle fiber region has a combination ofchopped strand glass fibers and microglass fibers. In some embodiments,the middle fiber region may contain between about 0 weight percent toabout 100 weight percent chopped strand glass fibers. In someembodiments, the middle fiber region may contain between about 5 weightpercent to about 15 weight percent chopped strand glass fibers. In someembodiments, the middle fiber region may contain between about 0 weightpercent to about 100 weight percent microglass fibers. In someembodiments, the middle fiber region may contain between about 85 weightpercent to about 95 weight percent microglass fibers. In someembodiments, the middle fiber region may contain between about 85 weightpercent to about 100 weight percent microglass fibers. In someembodiments, the middle fiber region may contain between about 60 weightpercent to about 85 weight percent microglass fibers. In someembodiments, the middle fiber region may contain between about 45 weightpercent to about 60 weight percent microglass fibers.

In some embodiments, each of the first and second peripheral fiberregions independently has a combination of chopped strand glass fibersand microglass fibers. In some embodiments, each of the first and secondperipheral fiber regions independently may contain between about 0weight percent to about 100 weight percent chopped strand glass fibers.In some embodiments, each of the first and second peripheral fiberregions independently may contain between about 5 weight percent toabout 15 weight percent chopped strand glass fibers. In someembodiments, each of the first and second peripheral fiber regionsindependently may contain between about 0 weight percent to about 100weight percent microglass fibers. In some embodiments, each of the firstand second peripheral fiber regions independently may contain betweenabout 85 weight percent to about 95 weight percent microglass fibers. Insome embodiments, each of the first and second peripheral fiber regionsindependently may contain between about 85 weight percent to about 100weight percent microglass fibers.

Other Materials

Additionally, the separators can include a variety of other materials ofconstruction. For example, the separator can include, in addition toglass fibers, non-glass fibers, natural fibers (e.g., cellulose fibers),synthetic fibers (e.g., polymeric), staple fibers, carbon fibers,nanofibers (electrospun, meltblown, centrifugal spun, etc.), fibrillatedfibers, pulps (e.g., wood pulps), binder resin, ceramic materials or anycombination thereof. Additionally, the fibers can include thermoplasticbinder fibers. Exemplary thermoplastic fibers include bicomponent,polymer-containing fibers, such as sheath-core fibers, side-by-sidefibers, “islands-in-the-sea” and/or “segmented-pie” fibers. Examples oftypes of polymeric fibers include substituted polymers, unsubstitutedpolymers, saturated polymers, unsaturated polymers (e.g., aromaticpolymers), organic polymers, inorganic polymers, straight chainedpolymers, branched polymers, homopolymers, copolymers, and combinationsthereof. Examples of polymer fibers include polyalkylenes (e.g.,polyethylene, polypropylene, polybutylene), polyesters (e.g.,polyethylene terephthalate), polyamides (e.g., nylons, aramids),halogenated polymers (e.g., polytetrafluoroethylenes), and combinationsthereof. Bicomponent fibers can be, e.g., from 1.3 to 15 decitex (weightin grams of 10,000 meters of fiber); can have a fiber length of e.g.,1-24 mm. In some embodiments, the middle fiber region may containbetween about 0 weight percent to about 30 weight percent of bicomponentfibers, (e.g., between about 1% and about 15%, between about 1% andabout 8%, between about 6% and about 8%, between about 6% and about 10%,between about 10% and about 15% or between about 10% and about 20%). Insome embodiments, each of the first and second peripheral fiber regionsindependently may contain between about 0 weight percent to about 30weight percent of bicomponent fibers, (e.g., between about 1% and about15%, between about 1% and about 8%, between about 6% and about 8%,between about 6% and about 10%, between about 10% and about 15% orbetween about 10% and about 20%).

Separator Characteristics

Surface Area

The BET surface area is measured according to method number 8 of BatteryCouncil International Standard BCIS-03A (2009 revision), “BCIRecommended Test Methods VRLA-AGM Battery Separators”, method number 8being “Surface Area.” Following this technique, the BET surface area ismeasured via adsorption analysis using a BET surface analyzer (e.g.,Micromeritics Gemini II 2370 Surface Area Analyzer) with nitrogen gas;the sample amount is between 0.5 and 0.6 grams in a ¾ inch tube; and,the sample is allowed to degas at 75° C. for a minimum of 3 hours.

In some embodiments, in which the middle fiber region contains at least1% by weight silica, the middle fiber region has a specific surfacearea, as measured using BET as described above, from about 1 to about 25m²/g, about 1 to about 15 m²/g, about 1 to about 10 m²/g, about 1 toabout 7 m²/g, about 2 to about 25 m²/g, about 2 to about 15 m²/g, about2 to about 10 m²/g or about 2 to about 7 m²/g.

In some embodiments, in which the middle fiber region contains both finefibers and at least 1% by weight silica, the middle fiber region has aspecific surface area, as measured using BET as described above, fromabout 1 to about 300 m²/g, about 1 to about 250 m²/g, about 1 to about200 m²/g, about 1 to about 150 m²/g, about 1 to about 100 m²/g, about 1to about 75 m²/g, about 1 to about 50 m²/g, about 1 to about 30 m²/g,about 1 to about 25 m²/g, about 2 to about 300 m²/g, about 2 to about250 m²/g, about 2 to about 200 m²/g, about 2 to about 150 m²/g, about 2to about 100 m²/g, about 2 to about 75 m²/g, about 2 to about 50 m²/g,about 2 to about 30 m²/g, about 2 to about 25 m²/g, about 3 to about 300m²/g, about 3 to about 250 m²/g, about 3 to about 200 m²/g, about 3 toabout 150 m²/g, about 3 to about 100 m²/g, about 3 to about 75 m²/g,about 3 to about 50 m²/g, about 3 to about 30 m²/g, about 3 to about 25m²/g, about 5 to about 300 m²/g, about 5 to about 250 m²/g, about 5 toabout 200 m²/g, about 5 to about 150 m²/g, about 5 to about 100 m²/g,about 5 to about 75 m²/g, about 5 to about 50 m²/g, about 5 to about 30m²/g, about 5 to about 25 m²/g, about 10 to about 300 m²/g, about 10 toabout 250 m²/g, about 10 to about 200 m²/g, about 10 to about 150 m²/g,about 10 to about 100 m²/g, about 10 to about 75 m²/g, about 01 to about50 m²/g, about 10 to about 30 m²/g or about 10 to about 25 m²/g.

In some embodiments, the specific surface area of each of the first andsecond peripheral fiber regions can independently range fromapproximately 1.0 m²/g to approximately 2.5 m²/g. For example, thespecific surface area of each of the first and second peripheral fiberregions can independently range from approximately 1.3 m²/g toapproximately 2.5 m²/g, from approximately 1.6 m²/g to approximately 2.5m²/g, from approximately 1.9 m²/g to approximately 2.5 m²/g, fromapproximately 1.3 m²/g to approximately 2.2 m²/g, from approximately 1.3m²/g to approximately 1.9 m²/g, or from approximately 1.6 m²/g toapproximately 2.2 m²/g. If filler particles are used in a peripheralfiber region, the specific surface area of that fiber region can begreater than or equal to 2 m²/g.

Other Characteristics

The basis weight, or grammage, of the separator can range fromapproximately 15 gsm (grams per square meter, or g/m²) to approximately500 gsm. In some embodiments, the basis weight ranges from betweenapproximately 20 gsm to approximately 100 gsm. In some embodiments, thebasis weight ranges from between approximately 100 gsm to approximately200 gsm. In some embodiments, the basis weight ranges from approximately200 gsm to approximately 300 gsm. In some embodiments, the basis weightof the separator ranges from between approximately 15 gsm toapproximately 100 gsm. The basis weight or grammage is measuredaccording to method number 3 “Grammage” of Battery Council InternationalStandard BCI5-03A (2009 Rev.) “BCI Recommended test Methods VRLA-AGMBattery Separators.”

In some embodiments, the thickness of the separator (i.e., from theouter end of the first peripheral fiber region to the outer end of thesecond peripheral fiber region) can vary. In some embodiments, thethickness of the separator can range from greater than zero to about 5millimeters. The thickness of the separator can be greater than or equalto about 0.1 mm, about 0.5 mm, about 1.0 mm, about 1.5 mm, about 2.0 mm,about 2.5 mm, about 3.0 mm, about 3.5 mm, about 4.0 mm, or about 4.5 mm;and/or less than or equal to about 5.0 mm, about 4.5 mm, about 4.0 mm,about 3.5 mm, about 3 mm, about 2.5 mm, about 2.0 mm, about 1.5 mm,about 1.0 mm, or about 0.5 mm. In some embodiments, the thickness of theseparator ranges from between about 0.1 mm to about 0.9 mm. Thethickness is measured according to method number 12 “Thickness” ofBattery Council International Standard BCI5-03A (2009 Rev.) “BCIRecommended test Methods VRLA-AGM Battery Separators.” This methodmeasures the thickness with a 1 square inch anvil load to a force of 10kPa (1.5 psi).

In some embodiments, the porosity of the separator is at least 80%, atleast 85%, at least 88%, or at least 90%. In some embodiments, theporosity of the separator ranges from 80% to 98%, from 85% to 97%, from88% to 95%, or from 90% to 95%. The porosity is measured according toBattery Council International Battery Technical Manual BCIS-03A (Rev.February 2002) (“Recommended Battery Materials Specifications: ValveRegulated Recombinant Batteries)”, method number 6, “Standard TestMethod for Volume Porosity of Recombinant Battery Separator Mats”.

Separator Performance

As described in Examples 1 and 2, various separators of the inventionwere made and tested against appropriate controls.

As noted, a 3-region separator in which the middle region comprisesabout 1 to 50% by weight fibers having an average diameter from about0.1 to less than 2 μm exhibits an improved tensile strength compared toa 3-region separator in which the middle region does not contain fibershaving such average diameter. As discussed in Example 2.1 and shown inFIGS. 1 and 2, a separator of the invention containing fine fiber in themiddle region exhibits increased tensile strength in both the machinedirection (about 22 to about 40% increase) and the cross direction(about 15 to about 37% increase) compared to the control (Example 1.3:3-region, no fine fiber or silica in the middle fiber region).

In some embodiments, the tensile strength (machine direction) of theseparator is about 2.00 to about 2.40 lbs/inch, about 2.00 to about 2.35lbs/inch, about 2.00 to about 2.30 lbs/inch, about 2.00 to about 2.25lbs/inch, about 2.00 to about 2.20 lbs/inch, about 2.05 to about 2.40lbs/inch, about 2.05 to about 2.35 lbs/inch, about 2.05 to about 2.30lbs/inch, about 2.05 to about 2.25 lbs/inch, or about 2.05 to about 2.20lbs/inch. The tensile strength is measured according to Battery CouncilInternational Battery Technical Manual BCIS-03A (Rev. February 2002)(“Recommended Battery Materials Specifications: Valve RegulatedRecombinant Batteries)”, method number 13, “Standard Test Method forTensile Strength and Percent Elongation Measurements on RecombinantBattery Separator Mat”.

In some embodiments, the tensile strength (cross direction) of theseparator is about 1.75 to about 2.20 lbs/inch, about 1.75 to about 2.15lbs/inch, about 1.75 to about 2.10 lbs/inch, about 1.75 to about 2.05lbs/inch, about 1.75 to about 2.00 lbs/inch, about 1.80 to about 2.20lbs/inch, about 1.80 to about 2.15 lbs/inch, about 1.80 to about 2.10lbs/inch, about 1.80 to about 2.05 lbs/inch, or about 1.80 to about 2.00lbs/inch. The tensile strength is measured according to BCIS-03A (Rev.February 2002), method number 13.

As shown in FIGS. 1, 2 and 6, while the presence of fine fiber in themiddle fiber region increases the acid filling time (also referred to as“acid filling speed”, “vacuum fill time”, “vacuum fill speed”, etc., andused interchangeably throughout) compared to the 3-region separatorhaving no fine fiber or silica in the middle fiber region, a separatorof the invention exhibits an increased tensile strength by comparison,and yet still provides a faster acid filling time (measured as describedin Example 2) compared to the control (Example 1.3: 3-region, no finefiber or silica in the middle fiber region). In this way a separator ofthe invention exhibits a balance of improved properties.

In some embodiments, a separator exhibits an acid filling time of about60 to about 155 seconds, and the tensile strength (machine direction) ofthe separator is about 2.00 to about 2.40 lbs/inch, about 2.00 to about2.35 lbs/inch, about 2.05 to about 2.40 lbs/inch, or about 2.05 to about2.35 lbs/inch. In some embodiments, a separator exhibits an acid fillingtime of about 75 to about 155 seconds, and the tensile strength (machinedirection) of the separator is about 2.00 to about 2.40 lbs/inch, about2.00 to about 2.35 lbs/inch, about 2.05 to about 2.40 lbs/inch, or about2.05 to about 2.35 lbs/inch. In some embodiments, a separator exhibitsan acid filling time of about 60 to about 130 seconds, and the tensilestrength (machine direction) of the separator is about 2.00 to about2.30 lbs/inch, about 2.00 to about 2.25 lbs/inch, about 2.05 to about2.30 lbs/inch, or about 2.05 to about 2.25 lbs/inch. In someembodiments, a separator exhibits an acid filling time of about 75 toabout 130 seconds, and the tensile strength (machine direction) of theseparator is about 2.00 to about 2.30 lbs/inch, about 2.00 to about 2.25lbs/inch, about 2.05 to about 2.30 lbs/inch, or about 2.05 to about 2.25lbs/inch. In some embodiments, a separator exhibits an acid filling timeof about 100 to about 155 seconds, and the tensile strength (machinedirection) of the separator is 2.15 to about 2.40 lbs/inch, about 2.15to about 2.35 lbs/inch, about 2.20 to about 2.40 lbs/inch, or about 2.20to about 2.35 lbs/inch. The tensile strength is measured according toBCIS-03A (Rev. February 2002), method number 13. The acid filling timeis measured as described in Example 2.

In some embodiments, a separator exhibits an acid filling time of about60 to about 155 seconds, and the tensile strength (cross direction) ofthe separator is about 1.75 to about 2.20 lbs/inch, about 1.75 to about2.15 lbs/inch, about 1.80 to about 2.20 lbs/inch, or about 1.80 to about2.15 lbs/inch. In some embodiments, a separator exhibits an acid fillingtime of about 75 to about 155 seconds, and the tensile strength (crossdirection) of the separator is about 1.75 to about 2.20 lbs/inch, about1.75 to about 2.15 lbs/inch, about 1.80 to about 2.20 lbs/inch, or about1.80 to about 2.15 lbs/inch. In some embodiments, a separator exhibitsan acid filling time of about 60 to about 130 seconds, and the tensilestrength (cross direction) of the separator is about 1.75 to about 2.10lbs/inch, about 1.75 to about 2.05 lbs/inch, about 1.80 to about 2.10lbs/inch, or about 1.80 to about 2.05 lbs/inch. In some embodiments, aseparator exhibits an acid filling time of about 75 to about 130seconds, and the tensile strength (cross direction) of the separator isabout 1.75 to about 2.10 lbs/inch, about 1.75 to about 2.05 lbs/inch,about 1.80 to about 2.10 lbs/inch, or about 1.80 to about 2.05 lbs/inch.In some embodiments, a separator exhibits an acid filling time of about100 to about 155 seconds, and the tensile strength (cross direction) ofthe separator is about 2.00 to about 2.20 lbs/inch, about 2.00 to about2.15 lbs/inch, about 1.95 to about 2.20 lbs/inch, or about 1.95 to about2.15 lbs/inch. The tensile strength is measured according to BCIS-03A(Rev. February 2002), method number 13. The acid filling time ismeasured as described in Example 2.

As shown in FIG. 3, a separator of the invention containing silica inthe middle region has increased surface area, measured according toBCIS-03A (2009 revision) method number 8, compared to the control(Example 1.3: 3-region, no fine fiber or silica in the middle fiberregion). As shown, the increase is significantly greater when theseparator contains both silica and fine fiber in the middle region.Without wishing to be bound by theory, it is believed that the finefiber further improves the retention rate of the silica.

As shown in FIGS. 3 and 7, while the presence of silica and/or finefiber in the middle fiber region increases the acid filling timecompared to the 3-region separator having no fine fiber or silica in themiddle fiber region (Example 1.3), a separator of the invention exhibitsan increased surface area by comparison, and yet still provides a fasteracid filling time (measured as described in Example 2) compared to thecontrol (Example 1.1: standard (high SSA)). In this way a separator ofthe invention exhibits a balance of improved properties.

In some embodiments in which the middle fiber region contains at least1% by weight silica, a separator of the invention has a middle fiberregion with a specific surface area from about 1 to about 10 m²/g, about1 to about 7 m²/g, about 2 to about 10 m²/g or about 2 to about 7 m²/g,and an acid filling speed of about 17 to about 50, about 17 to about 40,about 17 to about 30, about 20 to about 50, about 20 to about 40, about20 to about 30, about 25 to about 50, or about 25 to about 40 seconds(per 6 inches). The specific surface area is measured using BET asdescribed above, and the acid filling speed is measured as described inExample 2.

In some embodiments in which the middle fiber region contains both finefibers and at least 1% by weight silica, a separator of the inventionhas a middle fiber region with a specific surface area from about 2 toabout 30 m²/g, about 2 to about 25 m²/g, about 3 to about 30 m²/g, about3 to about 25 m²/g, about 5 to about 30 m²/g, about 5 to about 25 m²/g,about 10 to about 30 m²/g or about 10 to about 25 m²/g, and an acidfilling speed of about 35 to about 80, about 35 to about 70, about 35 toabout 60, about 35 to about 50, about 40 to about 80, about 40 to about70, about 40 to about 60, or about 40 to about 50 seconds (per 6inches). The specific surface area is measured using BET as describedabove, and the acid filling speed is measured as described in Example 2.

As shown in FIG. 4, a separator of the invention containing silica, finefiber or both silica and fine fiber in the middle region exhibitsincreased resistance to acid stratification, measured as described inExample 2 (compressed density 240 g/m²/mm), compared to the control(Example 1.3: 3-region, no fine fiber or silica in the middle fiberregion). As shown, the increase is significantly greater when theseparator contains both silica and fine fiber in the middle region.

As shown in FIGS. 4 and 7, while the presence of silica and/or finefiber in the middle fiber region increases the acid filling timecompared to the 3-region separator having no fine fiber or silica in themiddle fiber region (Example 1.3), a separator of the invention exhibitsan increased resistance to acid stratification, measured as described inExample 2 (compressed density 240 g/m²/mm), and yet still provides afaster acid filling time (measured as described in Example 2) comparedto the control (Example 1.1: standard (high SSA)). In this way aseparator of the invention exhibits a balance of improved properties.

In some embodiments, a separator of the invention has an acidstratification distance from about 2.5 to about 16 cm, about 3.0 toabout 16 cm, about 3.5 to about 16 cm, or about 3.5 to about 14 cm, andan acid filling speed of about 17 to about 50, about 17 to about 40,about 17 to about 30, about 20 to about 50, about 20 to about 40, about20 to about 30, about 25 to about 50, or about 25 to about 40 seconds(per 6 inches). Acid stratification distance and acid filling speed areeach measured as described in Example 2.

Processes

Making a Separator—Generally

A separator of the invention can be produced using a wet laid or a drylaid process. In general, a wet laid process involves mixing togetherthe fibers; for example, glass fibers (e.g., chopped strand and/ormicroglass) may be mixed together, optionally with any synthetic fibers,to provide a glass fiber slurry. In some cases, the slurry is anaqueous-based slurry. In certain embodiments, the microglass fibers, andoptionally any chopped strand and/or synthetic fibers, are storedseparately in various holding tanks prior to being mixed together. Thesefibers may be processed through a pulper before being mixed together. Insome embodiments, combinations of chopped strand glass fibers,microglass fibers, and/or synthetic fibers are processed through apulper and/or a holding tank prior to being mixed together. As discussedabove, microglass fibers may include fine microglass fibers and coarsemicroglass fibers.

It should be appreciated that any suitable method for creating a glassfiber slurry may be used. In some cases, additional additives are addedto the slurry to facilitate processing. The temperature may also beadjusted to a suitable range, for example, between 33° F./0.6° C. and100° F./38° C. (e.g., between 50° F./10° C. and 85° F./29° C.). In someembodiments, the temperature of the slurry is maintained. In some cases,the temperature is not actively adjusted.

In some embodiments, the wet laid process uses similar equipment as aconventional papermaking process, which includes a hydropulper, a formeror a headbox, a dryer, and an optional converter. For example, theslurry may be prepared in one or more pulpers. After appropriatelymixing the slurry in a pulper, the slurry may be pumped into a headbox,where the slurry may or may not be combined with other slurries oradditives may or may not be added. The slurry may also be diluted withadditional water such that the final concentration of fiber is in asuitable range, such as for example, between about 0.1% to 0.5% byweight.

In some cases, the pH of the glass fiber slurry may be adjusted asdesired. For instance, the pH of the glass fiber slurry may rangebetween about 1.5 and about 4.5, or between about 2.6 and about 3.2.

Before the slurry is sent to a headbox, the slurry may be passed throughcentrifugal cleaners for removing unfiberized glass or shot. The slurrymay or may not be passed through additional equipment such as refinersor deflakers to further enhance the dispersion of the fibers. Fibers maythen be collected on a screen or wire at an appropriate rate using anysuitable machine, e.g., a fourdrinier, a rotoformer, a cylinder, aninclined wire fourdrinier, a gap former, a twin wire, a multiply former,a pressure former, a top former, etc.).

In some embodiments, the process involves introducing binder (and/orother components) into a pre-formed glass fiber layer. In someembodiments, as the glass fiber layer is passed along an appropriatescreen or wire, different components included in the binder, which maybe in the form of separate emulsions, are added to the glass fiber layerusing a suitable technique. In some cases, each component of the binderresin is mixed as an emulsion prior to being combined with the othercomponents and/or glass fiber layer. In some embodiments, the componentsincluded in the binder may be pulled through the glass fiber layerusing, for example, gravity and/or vacuum. In some embodiments, one ormore of the components included in the binder resin may be diluted withsoftened water and pumped into the glass fiber layer.

In other embodiments, a dry laid process is used. In a dry laid process,glass fibers are chopped and dispersed in air that is blown onto aconveyor, and a binder is then applied. Dry laid processing is typicallymore suitable for the production of highly porous media includingbundles of glass fibers. In some embodiments, when the middle fiberregion is produced separately (to be laminated to the first and secondperipheral fiber regions), the middle fiber region is produced using adry laid process.

Any number of intermediate processes (e.g., pressing, calendering,laminating, etc.) and addition of additives may be utilized throughoutthe separator formation process. The silica of the middle region, whenpresent, can be added either to the slurry or to the separator as it isbeing formed. In some embodiments, the silica of the middle region, whenpresent, is added to the slurry. Additives can also be added either tothe slurry or to the separator as it is being formed, including salts,fillers including binders and latex. In some embodiments, the additivesmay comprise between about 0% to about 30% by weight of the separator.During the separator forming process, various pH values may be utilizedfor the slurries. Depending on the glass composition, the pH value mayrange from approximately 2 to approximately 4. Furthermore, the dryingtemperature may vary, also depending on the fiber composition. Invarious embodiments, the drying temperature may range from approximately100° C. to approximately 700° C. The separator may comprise more thanone layer, each layer optionally comprising different types of fiberswith different physical and chemical characteristics.

Multi-Phase Process

A multi-phase process may be used to make two or three regions of aseparator as a composite article. As an example, a three-regionseparator or a two-region portion thereof may be prepared by a wet laidprocess where a first fiber slurry (e.g., glass fibers in an aqueoussolvent such as water) is applied onto a wire conveyor to form a firstlayer. A second fiber slurry comprising fibers (e.g., glass fibers in anaqueous solvent such as water) is then applied onto the first layer.Vacuum may be continuously applied to the first and second slurriesduring the above process to remove solvent from the fibers, resulting inthe simultaneous formation of the first and second fiber regions into acomposite article. The composite article is then dried. Due to thisfabrication process, at least a portion of the fibers in the firstregion can be intermingled with at least a portion of the fibers fromthe second region (e.g., at the interface between the two layers), toform a transition zone. A third region can also be formed and addedusing a similar process or a different process such as lamination,co-pleating, or collation (i.e., placed directly adjacent one anotherand kept together by pressure). For example, in some cases, two layersare formed into a composite article by a wet laid process in whichseparate fiber slurries are laid one on top of the other as water isdrawn out of the slurry, and the composite article is then combined witha third layer by any suitable process (e.g., lamination, co-pleating, orcollation).

Thus, in one aspect the invention relates to a battery separator,comprising: a middle fiber region; a first peripheral fiber region; anda second peripheral fiber region; wherein the middle fiber region isdisposed between the first peripheral fiber region and the secondperipheral fiber region; and wherein the thickness of the middle fiberregion constitutes 1-49% of the total fiber region thickness; whereinthe first peripheral fiber region and at least a portion of the middlefiber region is produced by a process comprising: (a) providing a firstslurry of glass fibers having an average diameter from about 0.1 toabout 2 μm; (b) laying down the first slurry on a wire of a papermakingmachine; (c) providing a second slurry of (i) fibers having an averagediameter from 2 to about 50 μm, and (ii) fibers having an averagediameter from about 0.1 to less than 2 μm and/or silica; provided thatthe average diameter of the fibers of the second slurry is larger thanthe average diameter of the fibers of the first slurry; (d) laying downthe second slurry on top of the first slurry; and (e) dewatering thefirst and second slurries to form a 2-layer structure comprising thefirst peripheral fiber region and at least a portion of the middle fiberregion; such that the middle fiber region comprises: fibers having anaverage diameter from 2 to about 50 μm, and (i) from about 1 to 50% byweight fibers having an average diameter from about 0.1 to less than 2μm, or (ii) from about 1 to about 40% by weight silica, or (iii) fromabout 1 to about 40% by weight fibers having an average diameter fromabout 0.1 to less than 2 μm, and from about 1 to about 20% by weightsilica.

The multi-phase process can also include the use of one or more lamellasand more than one flow zone. For example, a system used to make theseparator (e.g., a papermaking machine) can include flow distributors(e.g., headboxes) configured to dispense one or more fiber slurries intoa flow zone positioned downstream of the one or more flow distributors.In some embodiments, a single flow distributor is present. In otherembodiments, two or more flow distributors can be present (e.g., forintroducing two or more fiber slurries into the system) In someembodiments, a distributor block can be positioned between the one ormore flow distributors and the flow zone. The distributor block may helpto evenly distribute the one or more fiber slurries across the width ofthe flow zone upon the slurry(ies) entering the flow zone. Differenttypes of distributor blocks are known in the art and can be used in theprocesses described herein.

A system used to make a separator of the invention (e.g., a papermakingmachine) can include a lamella positioned in the flow zone. The lamellamay be used as a partition to divide the flow zone into a lower portionand an upper portion (or into additional portions when multiple lamellasare present). In certain embodiments, the lamella can be used toseparate a first fiber slurry flowing in the lower portion of the flowzone from a second fiber slurry flowing in the upper portion of the flowzone. For example, a first fiber slurry dispensed from a first flowdistributor into the lower portion of the flow zone may be separatedfrom a second fiber slurry dispensed from a second flow distributor intothe upper portion of the flow zone until the mixtures reach a downstreamend of the lamella, after which the first and second fiber slurries areallowed to meet. The first and second fiber slurries generally flow inthe lower and upper portions of the flow zone in a downstream direction.

As described above, a lamella may be positioned in the flow zone topartition the flow zone into at least an upper portion and a bottomportion. A single lamella can be used, or the flow zone can include morethan one lamella for separating three or more fiber slurries. In somesuch embodiments, the flow zone can be separated into three, four, ormore distinct portions, each of which can contain a different fiberslurry or the same fiber slurry. The lamella can be positioned in anysuitable position within the flow zone, and can vary depending onrelative volumes of the fiber slurries in the upper and lower portionsof the flow zone. For example, the lamella can be positioned at thecenter of a distributor block to allow substantially equal volumesand/or flow velocities of the fiber slurries in each of the upper andlower portions of the flow zone, while in other embodiments the lamellacan be positioned higher or lower with respect to the distributor blockto allow a larger or smaller portion of one fiber slurry in the flowzone relative to the other. Furthermore, the lamella can be positionedat a slight decline with respect to the horizontal, or the lamella canbe substantially horizontal, or positioned at an incline with respect tothe horizontal. Other positions of the lamella in the flow zone are alsopossible.

A lamella can be attached to a portion of a system for forming theseparator using any suitable attachment technique. In some embodiments,a lamella is attached directly to a distributor block. In otherembodiments, a lamella is attached to a threaded rod positionedvertically within a portion of the flow zone. In certain embodiments,attachment involves the use of adhesives, fasteners, metallic bandingsystems, railing mechanisms, or other support mechanisms. Otherattachment mechanisms are also possible.

Forming the Three-region Separator

Any and all means of forming a middle fiber region disposed between twoperipheral fiber regions are contemplated to be within the scope of theinvention. For example, two fiber regions can be disposed adjacent toeach other as the result of a multi-phase process, such as thatdescribed above, in which the division of the regions is considered tobe at the midpoint of the transition zone. As discussed below, themidpoint of the transition zone is the midpoint of the densitydifferential between the two regions. The density differential can bedetermined by measuring the density gradient profile in thethicknesswise direction. Any suitable technique may be used to measurethe density gradient profile. One such method uses a QTRS Tree ringscanner and data analyzer model no. QTRS-01X (Quintek MeasurementSystems, Knoxville, Tenn.).

When a battery separator is made using a multi-phase forming process,the forming process causes fibers on the top phase to migrate andintermingle with fibers on the bottom phase, creating a transition zone.The apparent density of this zone may vary across the zone.

The apparent density (referred to as “density” herein) of a separator ismeasured as the grammage of the separator in g/m² per unit thickness ofthe separator (e.g., in gsm/mm). If the density of a separator isprofiled in the thickness direction (normal to the surface of theseparator), a gradient in density may be observed. This gradientindicates that the density of the separator decreases across the densityprofile from a region with fibers having a comparatively lower averagediameter (i.e., a peripheral fiber region) to a region with fibershaving a comparatively higher average diameter (i.e., the middle fiberregion) because the total void volume in the middle fiber region islarger than that of the peripheral fiber region. In the transition zone,across the density profile from peripheral fiber region to middle fiberregion, the density decreases from the peripheral fiber region to themiddle fiber region. The density gradient created as a result, can bemeasured as described above. Referring to the density profile dataobtained, the region where the density starts to change from one regionto the adjacent region is considered the transition zone. The midpointof the density differential between one region and the adjacent regionis the midpoint of the transition zone. An exemplary density profile andidentification of the midpoint of the transition zone between twoadjacent regions of a separator formed in a multi-phase papermakingprocess is shown in FIG. 9. The change in density of the separatoracross the middle fiber region, through the transition zone, and acrossthe peripheral fiber region is shown. As illustrated in FIG. 9, thedensity differential is the difference between the minimum density inthe middle fiber region and the maximum density in the peripheral fiberregion. The point at which the density profile reaches the midpoint ofthis differential (i.e., the density value that is half-way betweenthem) is the midpoint of the transition zone. The location on thethickness axis having the density of the midpoint of the transition zonedefines the end of each of the two fiber regions.

Alternatively, two separately-formed fiber regions can be laminated toeach other, in which case each of the regions may appear to be adiscrete layer. Combinations of a multi-phase process formation andlamination which result in the middle fiber region being disposedbetween the first peripheral fiber region and second peripheral fiberregion, wherein the thickness of the middle fiber region constitutes1-49% of the sum of the thicknesses of the middle fiber region, thefirst peripheral fiber region and the second peripheral fiber region arecontemplated to be within the scope of the invention.

In some embodiments, the separator is made by a multi-phase process, inwhich there is a first transition zone between the first peripheralfiber region and the middle fiber region, and there is a secondtransition zone between the middle fiber region and the secondperipheral fiber region. This embodiment is illustrated in FIG. 10A, inwhich a wavy line separating two regions indicates that there is atransition zone between the two regions. For this embodiment, in themulti-phase process described above, each “layer” formed is a fiberregion of the separator.

Thus, in one aspect the invention relates to a battery separator,comprising: a middle fiber region; a first peripheral fiber region; anda second peripheral fiber region; wherein the middle fiber region isdisposed between the first peripheral fiber region and the secondperipheral fiber region; and wherein the thickness of the middle fiberregion constitutes 1-49% of the total fiber region thickness; whereinthe battery separator is produced by a process comprising: (a) providinga first slurry of glass fibers having an average diameter from about 0.1to about 2 μm; (b) laying down the first slurry on a wire of apapermaking machine; (c) providing a second slurry of (i) fibers havingan average diameter from 2 to about 50 μm, and (ii) fibers having anaverage diameter from about 0.1 to less than 2 μm and/or silica;provided that the average diameter of the fibers of the second slurry islarger than the average diameter of the fibers of the first slurry; (d)laying down the second slurry on top of the first slurry; (e) providinga third slurry of glass fibers having an average diameter from about 0.1to about 2 μm; provided that the average diameter of the fibers of thethird slurry is smaller than the average diameter of the fibers of thesecond slurry; (f) laying down the third slurry on top of the secondslurry; and (g) dewatering the first, second and third slurries to formthe separator; such that the middle fiber region comprises: fibershaving an average diameter from 2 to about 50 μm, and (i) from about 1to 50% by weight fibers having an average diameter from about 0.1 toless than 2 μm, or (ii) from about 1 to about 40% by weight silica, or(iii) from about 1 to about 40% by weight fibers having an averagediameter from about 0.1 to less than 2 μm, and from about 1 to about 20%by weight silica.

In one aspect the invention relates to a process for forming a batteryseparator, comprising: a middle fiber region; a first peripheral fiberregion; and a second peripheral fiber region; wherein the middle fiberregion is disposed between the first peripheral fiber region and thesecond peripheral fiber region; the process comprising: (a) providing afirst slurry of glass fibers having an average diameter from about 0.1to about 2 μm; (b) laying down the first slurry on a wire of apapermaking machine; (c) providing a second slurry of (i) fibers havingan average diameter from 2 to about 50 μm, and (ii) fibers having anaverage diameter from about 0.1 to less than 2 μm and/or silica;provided that the average diameter of the fibers of the second slurry islarger than the average diameter of the fibers of the first slurry; (d)laying down the second slurry on top of the first slurry; (e) providinga third slurry of glass fibers having an average diameter from about 0.1to about 2 μm; provided that the average diameter of the fibers of thethird slurry is smaller than the average diameter of the fibers of thesecond slurry; (f) laying down the third slurry on top of the secondslurry; and (g) dewatering the first, second and third slurries to formthe separator, such that the thickness of the middle fiber regionconstitutes 1-49% of the sum of the thicknesses of the middle fiberregion and the first and second peripheral fiber regions; such that themiddle fiber region comprises: fibers having an average diameter from 2to about 50 μm, and (i) from about 1 to 50% by weight fibers having anaverage diameter from about 0.1 to less than 2 μm, or (ii) from about 1to about 40% by weight silica, or (iii) from about 1 to about 40% byweight fibers having an average diameter from about 0.1 to less than 2μm, and from about 1 to about 20% by weight silica.

In some embodiments, the separator is made by separately forming amiddle fiber layer, a first peripheral fiber layer and a secondperipheral fiber layer, and laminating the middle fiber layer to each ofthe peripheral fiber layers. This embodiment is illustrated in FIG. 10B,in which a dashed line separating two regions indicates that the tworegions have been separately formed and then joined together, so thatthere is no transition zone.

In some embodiments, the separator is made by separately forming a firstlayer comprising a first peripheral fiber region; separately forming asecond layer comprising a middle fiber region and a second peripheralfiber region by a multi-phase process, in which there is a transitionzone between the middle fiber region and the second peripheral fiberregion; and laminating the two layers together. This embodiment isillustrated in FIG. 10C, in which a dashed line separating two regionsindicates that the two regions have been separately formed and thenjoined together, so that there is no transition zone; and a wavy lineseparating two regions indicates that there is a transition zone betweenthe two regions. For this embodiment, in the multi-phase processdescribed above, each “layer” formed is a fiber region of the separator.

Thus, in one aspect the invention relates to a battery separator,comprising: a middle fiber region; a first peripheral fiber region; anda second peripheral fiber region; wherein the middle fiber region isdisposed between the first peripheral fiber region and the secondperipheral fiber region; and wherein the thickness of the middle fiberregion constitutes 1-49% of the total fiber region thickness; whereinthe battery separator is produced by a process comprising: (a) providinga first slurry of glass fibers having an average diameter from about 0.1to about 2 μm; (b) laying down the first slurry on a wire of apapermaking machine; (c) providing a second slurry of (i) fibers havingan average diameter from 2 to about 50 μm, and (ii) fibers having anaverage diameter from about 0.1 to less than 2 μm and/or silica;provided that the average diameter of the fibers of the second slurry islarger than the average diameter of the fibers of the first slurry; (d)laying down the second slurry on top of the first slurry; (e) dewateringthe first and second slurries to form a 2-layer structure comprising thefirst peripheral fiber region and the middle fiber region; (f) providinga fiber mat comprising glass fibers having an average diameter fromabout 0.1 to about 2 μm; provided that the average diameter of thefibers of the second slurry is larger than the average diameter of thefibers of the fiber mat; and (g) laminating the 2-layer structure formedin step (e) to the fiber mat to form the separator, wherein the 2-layerstructure comprises the first peripheral fiber region and the middleregion, and the fiber mat comprises the second peripheral fiber region;such that the middle fiber region comprises: fibers having an averagediameter from 2 to about 50 μm, and (i) from about 1 to 50% by weightfibers having an average diameter from about 0.1 to less than 2 μm, or(ii) from about 1 to about 40% by weight silica, or (iii) from about 1to about 40% by weight fibers having an average diameter from about 0.1to less than 2 μm, and from about 1 to about 20% by weight silica.

In one aspect the invention relates to a process for forming a batteryseparator comprising: a middle fiber region; a first peripheral fiberregion; and a second peripheral fiber region; wherein the middle fiberregion is disposed between the first peripheral fiber region and thesecond peripheral fiber region; the process comprising: (a) providing afirst slurry of glass fibers having an average diameter from about 0.1to about 2 μm; (b) laying down the first slurry on a wire of apapermaking machine; (c) providing a second slurry of (i) fibers havingan average diameter from about 2 to about 50 μm, and (ii) fibers havingan average diameter from about 0.1 to less than 2 μm and/or silica;provided that the average diameter of the fibers of the second slurry islarger than the average diameter of the fibers of the first slurry; (d)laying down the second slurry on top of the first slurry; (e) dewateringthe first and second slurries to form a 2-layer structure; (f) providinga fiber mat comprising glass fibers having an average diameter fromabout 0.1 to about 2 μm; provided that the average diameter of thefibers of the second slurry is larger than the average diameter of thefibers of the fiber mat; and (g) laminating the 2-layer structure formedin step (e) to the fiber mat to form the separator, wherein the 2-layerstructure comprises the first peripheral fiber region and the middlefiber region, and the fiber mat comprises the second peripheral fiberregion, such that the thickness of the middle fiber region constitutes1-49% of the sum of the thicknesses of the middle fiber region and thefirst and second peripheral fiber regions; such that the middle fiberregion comprises: fibers having an average diameter from 2 to about 50μm, and (i) from about 1 to 50% by weight fibers having an averagediameter from about 0.1 to less than 2 μm, or (ii) from about 1 to about40% by weight silica, or (iii) from about 1 to about 40% by weightfibers having an average diameter from about 0.1 to less than 2 μm, andfrom about 1 to about 20% by weight silica.

In some embodiments, the separator can be made by separately forming afirst layer comprising a first peripheral fiber region and a middlefiber region by a multi-phase process, in which there is a firsttransition zone between the first peripheral fiber region and the middlefiber region; separately forming a second layer comprising a middlefiber region and a second peripheral fiber region by a multi-phaseprocess, in which there is a second transition zone between the middlefiber region and the second peripheral fiber region; and laminating thetwo layers together such that the two separately formed middle fiberregions laminated together make up a single middle fiber region of theseparator. This embodiment is illustrated in FIG. 10D, in which a dashedline separating two regions indicates that the two regions have beenseparately formed and then joined together, so that there is notransition zone; and a wavy line separating two regions indicates thatthere is a transition zone between the two regions. For this embodiment,in the multi-phase process described above, each fine “layer” formed isa peripheral fiber region of the separator, while the two middle“layers” are combined to form the middle fiber region.

Thus, in one aspect the invention relates to a battery separator,comprising: a middle fiber region; a first peripheral fiber region; anda second peripheral fiber region; wherein the middle fiber region isdisposed between the first peripheral fiber region and the secondperipheral fiber region; and wherein the thickness of the middle fiberregion constitutes 1-49% of the total fiber region thickness; whereinthe battery separator is produced by a process comprising: (a) providinga first slurry of glass fibers having an average diameter from about 0.1to about 2 μm; (b) laying down the first slurry on a wire of apapermaking machine; (c) providing a second slurry of (i) fibers havingan average diameter from 2 to about 50 μm, and (ii) fibers having anaverage diameter from about 0.1 to less than 2 μm and/or silica;provided that the average diameter of the fibers of the second slurry islarger than the average diameter of the fibers of the first slurry; (d)laying down the second slurry on top of the first slurry; (e) dewateringthe first and second slurries to form a first 2-layer structurecomprising the first peripheral fiber region and a portion of the middlefiber region; (f) providing a third slurry of glass fibers having anaverage diameter from about 0.1 to about 2 μm; (g) laying down the thirdslurry on a wire of a papermaking machine (separate from the first andsecond slurries); (h) providing a fourth slurry of (I) fibers having anaverage diameter from 2 to about 50 μm, and (II) fibers having anaverage diameter from about 0.1 to less than 2 μm and/or silica;provided that the average diameter of the fibers of the fourth slurry islarger than the average diameter of the fibers of the third slurry; (i)laying down the fourth slurry on top of the third slurry; (j) dewateringthe third and fourth slurries to form a second 2-layer structurecomprising the second peripheral fiber region and a portion of themiddle fiber region; and (k) laminating the first 2-layer structure tothe second 2-layer structure to form the separator; such that the middlefiber region comprises: fibers having an average diameter from 2 toabout 50 μm, and (I) from about 1 to 50% by weight fibers having anaverage diameter from about 0.1 to less than 2 μm, or (III) from about 1to about 40% by weight silica, or (III) from about 1 to about 40% byweight fibers having an average diameter from about 0.1 to less than 2μm, and from about 1 to about 20% by weight silica.

Composition

In one aspect, the invention relates to a battery separator, comprising:a fiber region; and either (a) a silica-containing region adjacent tothe fiber region, or (b) a first silica-containing region and a secondsilica-containing region, wherein the fiber region is disposed betweenthe first silica-containing region and the second silica-containingregion; wherein the fiber region and each silica-containing regioncontains fibers having an average diameter from about 2 to about 25 μm;wherein the fiber region contains less than 2% (including 0%) by weightsilica; wherein each silica-containing region independently containsgreater than or equal to 2% by weight silica. In some embodiments, eachsilica-containing region independently contains 2 to about 30% by weightsilica. In some embodiments, the thickness of the fiber regionconstitutes greater than or equal to 25% of the total separatorthickness, and the thickness of the silica-containing region(s)constitutes greater than or equal to 30% of the total separatorthickness. In some embodiments, each silica-containing regionindependently contains about 5 to about 15% by weight silica.

As used herein in respect to such a separator, “total separatorthickness” refers to the sum of the thickness of the fiber region andthe thickness of the silica-containing region(s). The “thickness of thesilica-containing region(s)” refers to the thickness of the (one)silica-containing region, or the sum of the thicknesses of the firstsilica-containing region and the second silica-containing region, asapplicable.

The thickness of each region can be measured using any method describedabove, such as scanning electron microscopy (e.g., when two regions arelaminated together), or by measuring the density gradient profile (e.g.,when a multi-phase process is used). A silica-containing region willhave a higher density than the fiber region.

The silica of the silica-containing region(s) can be precipitatedsilica, colloidal silica and/or fumed silica. The silica has a surfacearea of at least 50 m²/g, e.g., from about 300 m²/g to about 510 m²/g,or from about 400 to about 510 m²/g. The average particle size of thesilica can be from about 0.001 to about 20 μm, e.g., from about 1 toabout 20 μm, from about 10 to about 20 μm, from about 2 to about 15 μm,or from about 7.5 to about 16 μm. In some embodiments, the silica isprecipitated silica. In some embodiments, the silica is fumed silica.

In some embodiments, the silica is precipitated silica having a surfacearea from about 50 to about 750 m²/g, about 100 to about 700 m²/g, about150 to about 650 m²/g, about 200 to about 600 m²/g, about 250 to about550 m²/g, about 300 to about 550 m²/g, about 300 to about 510 m²/g,about 350 to about 510 m²/g, or about 400 to about 510 m²/g. In someembodiments, the silica is precipitated silica having an averageparticle size from about 0.001 to about 20 μm, about 1 to about 20 μm,about 10 to about 20 μm, about 2 to about 15 μm, or about 7.5 to about16 μm. In some embodiments, the silica is precipitated silica having asurface area from about 50 to about 750 m²/g, about 100 to about 700m²/g, about 150 to about 650 m²/g, about 200 to about 600 m²/g, about250 to about 550 m²/g, about 300 to about 550 m²/g, about 300 to about510 m²/g, about 350 to about 510 m²/g, or about 400 to about 510 m²/g,and having an average particle size from about 0.001 to about 20 μm,about 1 to about 20 μm, about 10 to about 20 μm, about 2 to about 15 μm,or about 7.5 to about 16 μm. In some embodiments, the silica isprecipitated silica having a surface area from about 300 to about 510m²/g and an average particle size from about 1 to about 20 μm. In someembodiments, the silica is precipitated silica having a surface areafrom about 400 to about 510 m²/g and an average particle size from about7.5 to about 16 μm. In some embodiments, the silica is precipitatedsilica having a surface area from about 300 to about 750 m²/g and anaverage particle size from about 2 to about 15 μm. In some embodiments,the silica is precipitated silica having a surface area from about 450to about 750 m²/g and an average particle size from about 7.5 to about16 μm.

In some embodiments, the battery separator comprises: a fiber region;and a silica-containing region adjacent to the fiber region; wherein thefiber region and the silica-containing region contain fibers having anaverage diameter from about 2 to about 25 μm; wherein the fiber regioncontains less than 2% (including 0%) by weight silica; wherein thesilica-containing region contains 2 to about 30% by weight silica andwherein the thickness of the fiber region constitutes greater than orequal to 25% of the total separator thickness, and the thickness of thesilica-containing region constitutes greater than or equal to 30% of thetotal separator thickness. In some embodiments, the silica-containingregion contains about 5 to about 15% by weight silica.

In some embodiments, the battery separator comprises: a fiber region;and a first silica-containing region and a second silica-containingregion, wherein the fiber region is disposed between the firstsilica-containing region and the second silica-containing region;wherein the fiber region and each silica-containing region containsfibers having an average diameter from about 2 to about 25 μm; whereinthe fiber region contains less than 2% (including 0%) by weight silica;wherein each silica-containing region independently contains 2 to about30% by weight silica; and wherein the thickness of the fiber regionconstitutes greater than or equal to 25% of the total separatorthickness, and the thickness of the silica-containing regionsconstitutes greater than or equal to 30% of the total separatorthickness. In some embodiments, each silica-containing regionindependently contains about 5 to about 15% by weight silica.

In some embodiments, the thickness of the fiber region constitutesgreater than or equal to 25%, greater than or equal to 30%, greater thanor equal to 35%, greater than or equal to 40%, greater than or equal to45%, greater than or equal to 50%, greater than or equal to 55%, greaterthan or equal to 60%, greater than or equal to 65%, 25 to 70%, about 30to about 65%, about 30 to about 60%, about 30 to about 55%, about 30 toabout 50%, about 30 to about 45%, about 35 to about 55%, about 35 toabout 50% or about 40 to about 55% of the total separator thickness.

In some embodiments, each silica-containing region independentlycontains 2 to about 30%, about 3 to about 25%, about 4 to about 20% orabout 5 to about 15% by weight silica.

In some embodiments, the thickness of the silica-containing region(s)constitutes greater than or equal to 30%, greater than or equal to 35%,greater than or equal to 40%, greater than or equal to 45%, greater thanor equal to 50%, greater than or equal to 55%, greater than or equal to60%, greater than or equal to 65%, greater than or equal to 70%, 30 to75%, about 35 to about 70%, about 35 to about 65%, about 35 to about60%, about 35 to about 55%, about 35 to about 50%, about 40 to about70%, about 40 to about 65%, about 40 to about 60%, about 40 to about55%, about 45 to about 70%, about 45 to about 65%, about 45 to about60%, about 50 to about 70%, about 50 to about 65% or about 55 to about70% of the total separator thickness.

In some embodiments, the battery separator comprises a firstsilica-containing region and a second silica-containing region; thethickness of the first silica-containing region constitutes greater thanor equal to 10%, greater than or equal to 15% or greater than or equalto 20% of the total separator thickness; and the thickness of thesilica-containing regions constitutes greater than or equal to 30%,greater than or equal to 35%, greater than or equal to 40%, greater thanor equal to 45%, greater than or equal to 50%, greater than or equal to55%, greater than or equal to 60%, greater than or equal to 65%, greaterthan or equal to 70%, 30 to 75%, about 35 to about 70%, about 35 toabout 65%, about 35 to about 60%, about 35 to about 55%, about 35 toabout 50%, about 40 to about 70%, about 40 to about 65%, about 40 toabout 60%, about 40 to about 55%, about 45 to about 70%, about 45 toabout 65%, about 45 to about 60%, about 50 to about 70%, about 50 toabout 65% or about 55 to about 70% of the total separator thickness.

In some embodiments, the battery separator comprises a firstsilica-containing region and a second silica-containing region; thethickness of the first silica-containing region constitutes greater thanor equal to 10%, greater than or equal to 15% or greater than or equalto 20% of the total separator thickness; and the thickness of thesilica-containing regions constitutes greater than or equal to 30%,greater than or equal to 35%, greater than or equal to 40%, greater thanor equal to 45%, greater than or equal to 50%, greater than or equal to55%, greater than or equal to 60%, greater than or equal to 65%, greaterthan or equal to 70%, 30 to 75%, about 35 to about 70%, about 35 toabout 65%, about 35 to about 60%, about 35 to about 55%, about 35 toabout 50%, about 40 to about 70%, about 40 to about 65%, about 40 toabout 60%, about 40 to about 55%, about 45 to about 70%, about 45 toabout 65%, about 45 to about 60%, about 50 to about 70%, about 50 toabout 65% or about 55 to about 70% of the total separator thickness; andeach silica-containing region independently contains 2 to about 30%,about 3 to about 25%, about 4 to about 20% or about 5 to about 15% byweight silica.

In some embodiments, the fiber region and each silica-containing regioncontains fibers having an average diameter from about 2 to about 25 μm,about 2 to about 20 μm, about 2 to about 15 μm, about 2 to about 10 μm,about 3 to about 25 μm, about 3 to about 20 μm, about 3 to about 15 μm,about 3 to about 10 μm, about 4 to about 25 μm, about 4 to about 20 μm,about 4 to about 15 μm or about 4 to about 10 μm.

In some embodiments, the fiber region and each silica-containing regioncontains fibers having an average diameter from about 2 to about 25 μm,about 2 to about 20 μm, about 2 to about 15 μm, about 2 to about 10 μm,about 3 to about 25 μm, about 3 to about 20 μm, about 3 to about 15 μm,about 3 to about 10 μm, about 4 to about 25 μm, about 4 to about 20 μm,about 4 to about 15 μm or about 4 to about 10 μm; and the silica isprecipitated silica having a surface area from about 50 to about 750m²/g, about 100 to about 700 m²/g, about 150 to about 650 m²/g, about200 to about 600 m²/g, about 250 to about 550 m²/g, about 300 to about550 m²/g, about 300 to about 510 m²/g, about 350 to about 510 m²/g, orabout 400 to about 510 m²/g, and having an average particle size fromabout 0.001 to about 20 μm, about 1 to about 20 μm, about 10 to about 20μm, about 2 to about 15 μm, or about 7.5 to about 16 μm.

In some embodiments, a separator of the invention exhibits an acidstratification distance of about 4 to about 14 cm, about 4 to about 12cm, about 4 to about 10 cm, about 6 to about 14 cm, about 6 to about 12cm, about 6 to about 10 cm, about 8 to about 14 cm, about 8 to about 12cm, or about 8 to about 10 cm. The acid stratification distance ismeasured as described in Example 2.

In some embodiments, a separator of the invention exhibits an acidfilling speed of about 30 to about 70 seconds, about 30 to about 60seconds, about 30 to about 50 seconds, about 30 to about 40 seconds,about 35 to about 70 seconds, about 35 to about 60 seconds, or about 35to about 50 seconds. The acid filling speed is measured as described inExample 2.

In some embodiments, a separator of the invention exhibits an acidstratification distance of about 4 to about 14 cm, about 4 to about 12cm, about 4 to about 10 cm, about 6 to about 14 cm, about 6 to about 12cm, about 6 to about 10 cm, about 8 to about 14 cm, about 8 to about 12cm, or about 8 to about 10 cm, and exhibits an acid filling speed ofabout 30 to about 70 seconds, about 30 to about 60 seconds, about 30 toabout 50 seconds, about 30 to about 40 seconds, about 35 to about 70seconds, about 35 to about 60 seconds, or about 35 to about 50 seconds.The acid stratification distance and the acid filling speed are measuredas described in Example 2.

Any of the fibers described above can be used for the fibers of thefiber region.

Any of the processes described above can be used to make the separator.For example, fiber and silica-containing regions can be made separatelyas described, and then laminated into a two-layer (one silica-containingregion) or three-layer (two silica-containing regions) separator.Similarly, the wet laid process described above can be used to createthe separator by using separate stock flows for the fiber region and thesilica-containing region(s), in which the stock flow of the lattercontains the desired amount of silica.

Alternatively, a single-region separator can be made using any of theprocesses described above, and silica particles can be applied to theseparator to form one or two silica-containing regions. Any methodsuitable for such application of silica is contemplated to be within thescope of the invention. For example, silica particles can bepre-dispersed/suspended in a liquid (e.g., water), and the resultantsuspension can then be applied (e.g., by spraying or curtain coating,etc.) onto the pre-formed separator on either or both sides.

Batteries

In one aspect, the invention relates to a lead-acid battery comprising anegative plate, a positive plate, and any battery separator describedherein.

Thus, in one aspect, the invention relates to a lead-acid batterycomprising a negative plate, a positive plate, and a battery separatordisposed between the negative and positive plates, wherein the batteryseparator comprises: a middle fiber region; a first peripheral fiberregion; and a second peripheral fiber region; wherein the middle fiberregion comprises fibers having an average diameter from 2 to about 50μm; and (a) from about 1 to 50% by weight fibers having an averagediameter from about 0.1 to less than 2 μm, or (b) from about 1 to about40% by weight silica, or (c) from about 1 to about 40% by weight fibershaving an average diameter from about 0.1 to less than 2 μm, and fromabout 1 to about 20% by weight silica; wherein each of the first andsecond peripheral fiber regions independently comprises glass fibershaving an average diameter from about 0.1 to about 2 μm; wherein themiddle fiber region is disposed between the first peripheral fiberregion and second peripheral fiber region; and wherein the thickness ofthe middle fiber region constitutes 1-49% of the total fiber regionthickness.

In one aspect, the invention relates to a lead-acid battery comprising anegative plate, a positive plate, and a battery separator disposedbetween the negative and positive plates, wherein the battery separatorcomprises: a fiber region; and either (a) a silica-containing regionadjacent to the fiber region, or (b) a first silica-containing regionand a second silica-containing region, wherein the fiber region isdisposed between the first silica-containing region and the secondsilica-containing region; wherein the fiber region and eachsilica-containing region contains fibers having an average diameter fromabout 2 to about 25 μm; wherein the fiber region contains less than 2%(including 0%) by weight silica; wherein each silica-containing regionindependently contains greater than or equal to 2% by weight silica.

It is to be understood that the other components of the battery that arenot explicitly discussed herein can be conventional battery components.Positive plates and negative plates can be formed of conventional leadacid battery plate materials. For example, in container formattedbatteries, plates can include grids that include a conductive material,which can include, but is not limited to, lead, lead alloys, graphite,carbon, carbon foam, titanium, ceramics (such as Ebonex®), laminates andcomposite materials. The grids are typically pasted with activematerials. The pasted grids are typically converted to positive andnegative battery plates by a process called “formation.” Formationinvolves passing an electric current through an assembly of alternatingpositive and negative plates with separators between adjacent plateswhile the assembly is in a suitable electrolyte.

As a specific example, positive plates contain lead as the activematerial, and negative plates contain lead dioxide as the activematerial. Plates can also contain one or more reinforcing materials,such as chopped organic fibers (e.g., having an average length of 0.125inch or more), chopped glass fibers, metal sulfate(s) (e.g., nickelsulfate, copper sulfate), red lead (e.g., a Pb₃O₄-containing material),litharge, paraffin oil, and/or expander(s). In some embodiments, anexpander contains barium sulfate, carbon black and lignin sulfonate asthe primary components. The components of the expander(s) can bepre-mixed or not pre-mixed. Expanders are commercially available from,for example, Hammond Lead Products (Hammond, Ind.) and Atomized ProductsGroup, Inc. (Garland, Tex.). An example of a commercially availableexpander is Texex® expander (Atomized Products Group, Inc.). In certainembodiments, the expander(s), metal sulfate(s) and/or paraffin arepresent in positive plates, but not negative plates. In someembodiments, positive plates and/or negative plates contain fibrousmaterial or other glass compositions.

A battery can be assembled using any desired technique. For example,separators are wrapped around plates (e.g., cathode plates, anodeplates). positive plates, negative plates and separators are thenassembled in a case using conventional lead acid battery assemblymethods. In certain embodiments, separators are compressed after theyare assembled in the case, i.e., the thickness of the separators arereduced after they are placed into the case. An electrolytic mixture(e.g., just sulfuric acid, or sulfuric acid and silica, sulfuric acidand particles of the glass compositions described herein, etc.) is thendisposed in the case.

The electrolytic mixture can include other compositions. For example,the electrolytic mixture can include liquids other than sulfuric acid,such as a hydroxide (e.g., potassium hydroxide). In some embodiments,the electrolytic mixture includes one or more additives, including butnot limited to a mixture of an iron chelate and a magnesium salt orchelate, organic polymers and lignin and/or organic molecules, andphosphoric acid. In some embodiments, the electrolyte is sulfuric acid.In some embodiments, the specific gravity of the sulfuric acid isbetween 1.21 g/cm³ and 1.32 g/cm³, or between 1.28 g/cm³ and 1.31 g/cm³.In certain embodiments the specific gravity of the sulfuric acid is 1.26g/cm³. In certain embodiments the specific gravity of the sulfuric acidis about 1.3 g/cm³.

EXAMPLES Example 1. Separators Example 1.1. High Surface Area ControlSeparator

The high surface area control separator (“standard (high SSA)”) used inExample 2 has the following composition (all percentages are by weight):86% glass microfibers (diameter 0.8 to 1.4 μm, average diameter 1.1 μm),8% PET core/PE sheath bicomponent organic fibers (1.3 DTEX, 12 mm long),6% chop strand (13.5 μm dia, ½ inch long) glass fibers.

Example 1.2. Low Surface Area Control Separator

The low surface area control separator (“standard (low SSA)”) used inExample 2 has the following composition (all percentages are by weight):86% glass microfiber (diameter 0.8 to 1.9 μm, average diameter 1.5 μm),8% PET core/PE sheath bicomponent organic fibers (1.3 DTEX, 12 mm long),6% chop strand (13.5 μm dia, ½ inch long) glass fibers.

Example 1.3. Three-Region Control Separator

The three-region control separator (“3-region”) used in Example 2 wasmade by laminating the middle fiber region (about 40% by weight, madefrom Composition B) between two peripheral fiber regions (made fromComposition A):

-   -   Composition A (peripheral fiber region) (all percentages are by        weight): 86% glass microfibers (diameter 0.8 to 1.4 μm, average        diameter 1.1 μm), 8% PET core/PE sheath bicomponent organic        fibers (1.3 DTEX, 12 mm long), 6% chop strand (13.5 μm dia, ½        inch long) glass fibers;    -   Composition B (middle fiber region) (all percentages are by        weight): 86% glass microfiber (diameter 8.5 μm), 8% PET core/PE        sheath bicomponent organic fibers (1.3 DTEX, 12 mm long), 6%        chop strand (13.5 μm dia, ½ inch long) glass fibers.

Example 1.4. Three-Region Separators (Laminated)

Each of the three-region separators used in Example 2 was made bylaminating the appropriate middle fiber region (about 40% by weight,made from Composition B1, B2, B3, B4, B5, B6 or B7) between twoperipheral fiber regions (made from Composition A):

-   -   Composition A (peripheral fiber region) (all percentages are by        weight): 86% glass microfibers (diameter 0.8 to 1.4 μm, average        diameter 1.1 μm), 8% PET core/PE sheath bicomponent organic        fibers (1.3 DTEX, 12 mm long), 6% chop strand (13.5 μm dia, ½        inch long) glass fibers;    -   Composition B1 (middle fiber region+silica) (all percentages are        by weight): 76.6% glass microfiber (diameter 8.5 μm), 8% PET        core/PE sheath bicomponent organic fibers (1.3 DTEX, 12 mm        long), 5.4% chop strand (13.5 μm dia, ½ inch long) glass fibers,        10% silica (Sipernat® 50S, BET surface area of 475 m²/g);    -   Composition B2 (middle fiber region+fine fiber) (all percentages        are by weight): 76.6% glass microfiber (diameter 8.5 μm), 8% PET        core/PE sheath bicomponent organic fibers (1.3 DTEX, 12 mm        long), 5.4% chop strand (13.5 μm dia, ½ inch long) glass fibers,        10% glass microfiber (diameter 1.4 μm);    -   Composition B3 (middle fiber region+fine fiber+silica) (all        percentages are by weight): 67.3% glass microfiber (diameter 8.5        μm), 8% PET core/PE sheath bicomponent organic fibers (1.3 DTEX,        12 mm long), 4.7% chop strand (13.5 μm dia, ½ inch long) glass        fibers, 10% glass microfiber (diameter 1.4 μm), 10% silica        (Sipernat® 50S, BET surface area of 475 m²/g);    -   Composition B4 (middle fiber region+12.5% fine fiber) (all        percentages are by weight): 74.3% glass microfiber (diameter 8.5        μm), 8% PET core/PE sheath bicomponent organic fibers (1.3 DTEX,        12 mm long), 5.2% chop strand (13.5 μm dia, ½ inch long) glass        fibers, 12.5% glass microfiber (diameter 1.4 μm);    -   Composition B5 (middle fiber region+25% fine fiber) (all        percentages are by weight): 62.6% glass microfiber (diameter 8.5        μm), 8% PET core/PE sheath bicomponent organic fibers (1.3 DTEX,        12 mm long), 4.4% chop strand (13.5 μm dia, ½ inch long) glass        fibers, 25% glass microfiber (diameter 1.4 μm);    -   Composition B6 (middle fiber region+37.5% fine fiber) (all        percentages are by weight): 51.0% glass microfiber (diameter 8.5        μm), 8% PET core/PE sheath bicomponent organic fibers (1.3 DTEX,        12 mm long), 3.5% chop strand (13.5 μm dia, ½ inch long) glass        fibers, 37.5% glass microfiber (diameter 1.4 μm);    -   Composition B7 (middle fiber region+50% fine fiber) (all        percentages are by weight): 39.3% glass microfiber (diameter 8.5        μm), 8% PET core/PE sheath bicomponent organic fibers (1.3 DTEX,        12 mm long), 2.7% chop strand (13.5 μm dia, ½ inch long) glass        fibers, 50% glass microfiber (diameter 1.4 μm);

Example 1.5. Three-Region Separators

Separators of the invention can also be made by using a multi-phaseprocess or a multi-phase+lamination process as described above. Forexample, the separators described in Example 1.4 can be made using thefollowing procedure, where “Composition B” refers to Composition B1, B2,B3, B4, B5, B6 or B7, as appropriate.

Fibers for Composition A are added to a hydropulper one by onecontaining water and sulfuric acid to form a fiber dispersion slurry.The pH is maintained at 2.7. The fiber slurry is stored in a chest(tank) under agitation. The same process is repeated for Composition Band the fiber slurry thus prepared is stored in a second chest underagitation. The two chests supply the slurries to the pressurized headboxof the paper machine (Fourdrinier). Composition A forms the bottom flowand Composition B forms the top flow in the pressurized headbox. The twoflows are separated by a lamella. Composition A is the first layer tocontact the wire of the forming zone using dewatering (vacuum). Furtherdown the wire, the point where lamella ends, Composition B contacts thetop of Composition A, thus creating a two layer structure with 100 gsmof peripheral fiber region (composition A) as base and 20 gsm of middlefiber region (composition B) as top. Vacuum is used to dewater the twolayer separator. The two layer separator is then dried using steamheated drier cans and a through-air dryer (hot air causes melting ofsheath of bico fibers and creates bonding between organic fiber andglass fibers). The two-layer battery separator is collected at the otherend of the machine on rolls. The two-layer separator thus made, is thenlaminated to a single layer battery separator (made from Composition A,forming the second peripheral fiber region) wherein the middle region ofthe two layer separator is in physical contact with the single layerseparator. A three-region separator is thus created with the middlefiber region disposed between two peripheral fiber regions.

Example 2. Measurement of Separator Properties Example 2.1. Measurementof Tensile Strength

The tensile strength is measured according to Battery CouncilInternational Battery Technical Manual BCIS-03A (Rev. February 2002)(“Recommended Battery Materials Specifications: Valve RegulatedRecombinant Batteries)”, method number 13, “Standard Test Method forTensile Strength and Percent Elongation Measurements on RecombinantBattery Separator Mat”, incorporated by reference herein in itsentirety.

The tensile strength of various separators of the invention and the3-region control separator (Example 1.3) was measured. Separators of theinvention tested had the same composition as the control plus the amountof fine fiber in the middle region indicated in the table below.

% by weight fine fiber Tensile Tensile (1.4 μm diameter glass StrengthStrength fiber) in middle region (MD) (lb/in) (CD) (lb/in) 0 (control)1.69 1.56 12.5 2.06 1.80 25 2.19 1.99 37.5 2.29 2.11 50 2.36 2.14

As shown in the table above and in FIGS. 1 and 2, the tested separatorsof the invention exhibited about a 22 to 40% increase in tensilestrength (MD), and about a 15 to 37% increase in tensile strength (CD)compared to the control separator.

Example 2.2. Measurement of Acid Diffusion Speed

The speed at which sulfuric acid diffuses in a separator while undercompression can be measured using the following procedure. The measureddiffusion speed can provide an indication of potential acid fillingspeed and separator wettability within a battery cell.

Equipment

Methyl red, diluted in 1.28 specific gravity sulfuric acid (1:100dilution)

Glass-mat separator (AGM)

300×150×50 mm Perspex blocks, with holes drilled for attaching

Screw-thread, nuts and washers

Shims, various thicknesses, for the required gap

Rubber gasket or O-ring cord, various diameters, for ‘sealing’ thesample

Pyrex dish to hold block assembly

Timer/stopwatch

Sample Preparation

-   1. Measure the grammage of the separator, to one decimal point, in    g/m² (W).-   2. Measurements of diffusion speed are typically made at about 200    g/m²/mm compressed density and/or about 240 g/m²/mm compressed    density.-   3. Calculate the required thickness for each density value:    -   3.1. Thickness=grammage÷compressed density (either 200 or 240).-   4. Determine the shims and o-ring cords required for each thickness    calculated:    -   4.1. Shims should be to the nearest available thickness        increment.    -   4.2. O-ring cord diameter should be equal to, or greater than,        the shim thickness, but no more than 0.5 mm greater.-   5. Cut two samples of separator, 250×50 mm, in the machine    direction.-   6. Put the bolts through the Perspex base and lay the assembly on    the bench.-   7. Place dry sample on the Perspex base.-   8. Align the o-ring cords tight to the edges of the separator.-   9. Put the required shims onto each bolt.-   10. Add the Perspex face to the top of this assembly and    finger-tighten the nuts.-   11. Push the o-ring cords tightly to the sample edge all along the    AGM, particularly at the top.-   12. Tighten the nuts using the torque wrench (set at 10 Nm/88.5    in/lbf).    -   (refer to FIG. 5A.)

Sample Testing

-   13. Put the full block in an empty Pyrex dish.-   14. Add dyed sulfuric acid (SG 1.28 g/cm²) into the space at the top    of the sample and start the timer (60-minute countdown).-   15. The acid will travel or diffuse through the pores of the    separator and a visual red/pink ‘tide mark’ will be observed,    displaying the magnitude of displacement or diffusion.-   16. Check the status of the displacement at regular intervals (every    1 minute initially; varies with sample).-   17. After the 60 minutes is completed, measure the total acid    displacement (distance from the top of the sample to the red/pink    mark).-   18. Report diffusion speed, at each density measured, in terms of    average time in seconds for the acid front to reach 6 cm from top of    the sample.

Example 2.3. Measurement of Vacuum Fill (Acid Filling) Time

Equipment

1.28 specific gravity sulfuric acid

Glass-mat separator (AGM)

6″×1.9375″ Die

300×150×50 mm Perspex blocks, with holes drilled for attaching

Screw-thread, nuts and washers

Shims, various thicknesses, for the required gap

Rubber gasket or O-ring cord for ‘sealing’ the sample

Acid feed assembly (cut bottles with tubing), including stand and clamps

Vacuum pump

Timer/stopwatch

Sample Preparation

-   1. Measure the grammage of the separator, to one decimal point, in    g/m² (W).-   2. Calculate the required thickness for each density value:    -   2.1. Thickness=grammage÷compressed density (either 200 or 240).-   3. Determine the shims and o-ring cords required for each thickness    calculated:    -   3.1. Shims should be to the nearest available thickness        increment.    -   3.2. O-ring cord diameter should be equal to, or greater than,        the shim thickness, but no more than 0.5 mm greater.-   4. Use the 6″×1.9375″ die to cut the sample in the machine    direction.-   5. Weigh the sample to determine the amount of acid needed.-   6. Mark the sample at every inch.-   7. Put the bolts through the Perspex base and lay the assembly on    the bench.-   8. Place the sample on the Perspex base in between the grooves on    the plate.-   9. Align the rubber gasket on the edges of the separator in the    grooves on the plate.-   10. Put the required shims onto each bolt.-   11. Add the Perspex face to the top of this assembly and    finger-tighten the nuts.-   12. Tighten the nuts using the torque wrench (set at 10 N).    -   (refer to FIG. 5B.)

Sample Testing

-   13. Stand the block upright and plug in the acid feed assembly.-   14. Add the appropriate amount of acid to the top of the feed    system. Make sure the valve is closed.-   15. Turn the vacuum pump on and pump down to 530 mm Hg.-   16. When the system reaches the correct pressure, open up the valve    to the acid and record the acid front travel time at every inch.

Example 2.4. Measurement of Acid Stratification Distance

This method is used to determine the degree to which sulfuric aciddisplaces water in a glass-mat separator while under compression. Themeasured stratification distance can provide an indication of potentialstratification within a battery cell, a phenomenon in which the specificgravity of the electrolyte (acid) varies throughout the height of thecell.

Equipment

Methyl red, diluted in 1.28 specific gravity sulfuric acid (1:100dilution)

1.1 specific gravity sulfuric acid

Glass-mat separator (AGM)

300×150×50 mm Perspex blocks, with holes drilled for attaching

Screw-thread, nuts and washers

Shims, various thicknesses, for the required gap

Rubber gasket or O-ring cord, various diameters, for ‘sealing’ thesample

Pyrex dish to hold block assembly and acid

Timer/stopwatch

Sample Preparation

-   1. Measure the grammage of the separator, to one decimal point, in    g/m² (W).-   2. Measurements of acid stratification distance are typically made    at about 200 g/m²/mm compressed density and/or about 240 g/m²/mm    compressed density.-   3. Calculate the required thickness for each density value:    -   3.1. Thickness=grammage÷ compressed density (either 200 or 240).-   4. Determine the shims and o-ring cords required for each thickness    calculated:    -   4.1. Shims should be to the nearest available thickness        increment.    -   4.2. O-ring cord diameter should be equal to, or greater than,        the shim thickness, but no more than 0.5 mm greater.-   5. Cut two samples of separator, 250×50 mm, in the machine    direction.-   6. Immerse the sample in 1.1 s.g. acid for one minute.-   7. Put the bolts through the Perspex base and lay the assembly on    the bench.-   8. Place wet sample on the Perspex base.-   9. Align the o-ring cords tight to the edges of the separator.-   10. Put the required shims onto each bolt.-   11. Add the Perspex face to the top of this assembly and    finger-tighten the nuts.-   12. Push the o-ring cords tightly to the sample edge all along the    AGM, particularly at the top.-   13. Tighten the nuts using the torque wrench (set at 10 Nm/88.5    in/lbf).    -   (refer to FIG. 8.)

Sample testing

-   14. Put the full block in an empty Pyrex dish with a 20 mm 1.1 s.g.    acid level.-   15. Add dyed sulfuric acid (SG 1.28 g/cm²) into the space at the top    of the sample and start the timer (60-minute countdown).-   16. The acid will travel or diffuse through the pores of the    separator and a visual red/pink ‘tide mark’ will be observed,    displaying the magnitude of displacement.-   17. Check the status of the displacement at regular intervals (every    15 minutes is sufficient).-   18. After the 60 minutes is completed, measure the total acid    displacement (distance from the top of the sample to the red/pink    mark).-   19. Report acid stratification distance, at each density measured in    mm.    3. Three-Region Separator.

The furnishes used to form hand sheets with and without silica particlesare shown in the table below.

AGM AGM-SiO₂ Raw Materials (% by weight) (% by weight) Glass fiber-1(diameter: 1.4 μm) 22.00 19.80 Glass fiber-2 (diameter: 0.8 μm) 10.009.00 Glass fiber-3 (diameter: 8.5 μm) 46.90 42.21 Bicomponentpolyester/polyethylene fiber 15.50 13.95 (diameter: 13 μm) Glass fiberchopped strand 5.60 5.04 (diameter: 13.5 μm) Precipitated silica(average particle size: 9.85 16 μm; specific surface area, 485 m²/g)Guar gum-based flocculating agent 0.23 Totals 100 100

The hand sheets based on the above furnishes were formed according tothe following procedures.

Formation of AGM Hand Sheets.

-   1. Fill a laboratory-scale stainless steel pulper (capacity: 45 L)    with 27 L water and 41 mL of 25% sulfuric acid.-   2. Add glass fiber-1 and glass fiber-2 into the pulper and start    mixing for 5 min under the setting (8).-   3. Add glass fiber-3 into the pulper and start mixing for 5 min    under the setting (4).-   4. Add chopped strand glass fibers and Bicomponent fibers into the    pulper and start mixing for 5 min under the setting (4).-   5. Fill a laboratory-scale cubic headbox (12″×12″×12″) and add 10 mL    of 25% sulfuric acid.-   6. Measure out stock (GSM target: 135) and add to headbox, drained,    vacuum; between sheets, keep the pulper stirring.-   7. Dry the sheet in photo drier at 90° C. for 2 h.-   8. Dry the sheet at 150° C. for 2 min.

Formation of AGM-SiO₂ Hand Sheets.

-   1. Fill a laboratory-scale stainless steel pulper (capacity: 45 L)    with 27 L water and 41 mL of 25% sulfuric acid.-   2. Add glass fiber-1 and glass fiber-2 into the pulper and start    mixing for 5 min under the setting (8).-   3. Add glass fiber-3 and silica into the pulper and start mixing for    5 min under the setting (4).-   4. Add chopped strand glass fibers and Bicomponent fibers into the    pulper and start mixing for 5 min under the setting (4).-   5. Set the mixer speed to setting (2) and slowly add the    flocculating agent solution in 30 sec.-   6. After adding the flocculating agent keep stirring the pulper at    the low (2) setting for anther 5 min.-   7. Fill the headbox and add 10 mL of 25% sulfuric acid.-   8. Measure out stock (GSM target: 135) and add to headbox, drained,    vacuum; between sheets, keep the pulper stirring.-   9. Dry the sheet in photo drier at 90° C. for 2 h.-   10. Dry the sheet at 150° C. for 2 min.

Properties of these hand sheets are shown in the table below.

Properties AGM AGM-SiO₂ gsm 134.8 133.7 Thickness (mm) 0.85 0.79 Density(gsm/mm) 160.6 170.1 Air permeability (CFM) 20.3 12.9 Max pore (micron)48.5 42.5 Specific surface area (m²/g) 0.73 25.12

A 3-region separator was created by laminating the sheets asAGM-SiO₂/AGM/AGM-SiO₂. A reference AGM/AGM/AGM separator was alsocreated.

The acid stratification distance of each separator was measured asdescribed in Example 2 (compressed density 240 g/m²/mm). The referenceAGM/AGM/AGM separator showed an average (of 2 runs) travel distance of17.5 cm, while the AGM-SiO₂/AGM/AGM-SiO₂ separator showed an average (of2 runs) travel distance of 9.0 cm. This represents about a 50% decreasein acid stratification distance, i.e., about a 50% improvement inresistance to acid stratification.

The acid filling speed of each separator was measured as described inExample 2 (compressed density 200 g/m²/mm). The reference AGM/AGM/AGMseparator showed an average (of 2 runs) acid filling time of about 27.5seconds, while the AGM-SiO₂/AGM/AGM-SiO₂ separator showed an average (of2 runs) acid filling time of about 34.5 seconds. This represents about a25% decrease in acid filling time.

Thus, it is shown that a separator of the invention exhibits about a 50%improvement in resistance to acid stratification with only about a 25%decrease in acid filling time. In this way a separator of the inventionexhibits a balanced improvement in properties.

What is claimed is:
 1. A battery separator, comprising: a middle fiberregion; a first peripheral fiber region; and a second peripheral fiberregion; wherein the middle fiber region comprises fibers having anaverage diameter from 2 to about 50 μm; and wherein each of the firstand second peripheral fiber regions independently comprises glass fibershaving an average diameter from about 0.1 to about 2 μm; provided thatthe average diameter of the fibers of the middle fiber region is largerthan the average diameter of the fibers of each of the first and secondperipheral fiber regions; wherein the middle fiber region is disposedbetween the first peripheral fiber region and the second peripheralfiber region; wherein the thickness of the middle fiber regionconstitutes 1-49% of the total fiber region thickness; and wherein theseparator exhibits an acid filling time of about 17 to about 155seconds.
 2. The battery separator according to claim 1, wherein themiddle fiber region comprises glass fibers having an average diameterfrom 2 to about 50 μm.
 3. The battery separator according to claim 1,wherein the middle fiber region comprises fibers having an averagediameter from about 3 to about 15 μm.
 4. The battery separator accordingto claim 1, wherein the middle fiber region comprises glass fibershaving an average diameter from about 3 to about 15 μm.
 5. The batteryseparator according to claim 1, wherein each of the first and secondperipheral fiber regions independently comprises glass fibers having anaverage diameter from about 0.4 to about 1.8 μm.
 6. The batteryseparator according to claim 1, wherein the thickness of the middlefiber region constitutes 10-40% of the total fiber region thickness. 7.The battery separator according to claim 1, wherein the middle fiberregion comprises from about 10 to 30% by weight fibers having an averagediameter from about 0.1 to less than 2 μm.
 8. The battery separatoraccording to claim 1, wherein the middle fiber region comprises fromabout 10 to about 30% by weight fibers having an average diameter fromabout 0.8 to about 1.6 μm.
 9. The battery separator according to claim1, wherein the middle fiber region comprises from about 2 to about 30%by weight silica.
 10. The battery separator according to claim 1,wherein the average glass fiber diameter of the first peripheral fiberregion differs from the average glass fiber diameter of the secondperipheral fiber region by greater than or equal to 0.5 μm.
 11. Thebattery separator according to claim 1, wherein the middle fiber regioncomprises from about 1 to 50% by weight fibers having an averagediameter from about 0.1 to less than 2 μm, and wherein the tensilestrength (machine direction) of the separator is about 2.00 to about2.40 lbs/inch.
 12. The battery separator according to claim 1, whereinthe middle fiber region comprises from about 1 to 50% by weight fibershaving an average diameter from about 0.1 to less than 2 μm, and whereinthe tensile strength (cross direction) of the separator is about 1.75 toabout 2.20 lbs/inch.
 13. The battery separator according to claim 1,wherein the separator exhibits an acid filling time of about 30 to about70 seconds.
 14. The battery separator according to claim 1, wherein theseparator exhibits an acid stratification distance from about 2.5 toabout 16 cm.
 15. A lead-acid battery comprising a negative plate, apositive plate, and a battery separator according to claim 1, whereinthe battery separator is disposed between the negative and positiveplates.
 16. The battery separator according to claim 1, wherein themiddle fiber region comprises from about 5 to about 50% by weight glassfibers having an average diameter from about 0.1 to less than 2 μm. 17.The battery separator according to claim 1, wherein the middle fiberregion comprises from about 5 to about 50% by weight glass fibers havingan average diameter from about 0.8 to about 1.6 μm.
 18. The batteryseparator according to claim 17, wherein the separator exhibits an acidfilling time of about 17 to about 50 seconds.
 19. The battery separatoraccording to claim 1, wherein the middle fiber region comprises fromabout 1 to 50% by weight glass fibers having an average diameter fromabout 0.1 to less than 2 μm, and wherein the tensile strength (machinedirection) of the separator is about 2.00 to about 2.40 lbs/inch and/orthe tensile strength (cross direction) of the separator is about 1.75 toabout 2.20 lbs/inch.
 20. A battery separator, comprising: a middle fiberregion; a first peripheral fiber region; and a second peripheral fiberregion; wherein the middle fiber region comprises fibers having anaverage diameter from 2 to about 50 μm; and wherein each of the firstand second peripheral fiber regions independently comprises glass fibershaving an average diameter from about 0.1 to about 2 μm; provided thatthe average diameter of the fibers of the middle fiber region is largerthan the average diameter of the fibers of each of the first and secondperipheral fiber regions; wherein the middle fiber region is disposedbetween the first peripheral fiber region and the second peripheralfiber region; wherein the thickness of the middle fiber regionconstitutes 1-49% of the total fiber region thickness; and wherein theseparator exhibits an acid stratification distance from about 2.5 toabout 16 cm.